Use a template for PD message headers

The new tempate variable sets the data role, power role, and
specification revision in one fell swoop.  It's used by the PE and DPM
alike for creating messages, and in the future it may have a part in
determining if we're doing PD 2.0 or 3.0.

lib/include/pdb_pe.h

 
     /* PE mailbox for received PD messages */
     mailbox_t mailbox;
+    /* PD message header template */
+    uint16_t hdr_template;
 
     /* The received message we're currently working with */
     union pd_msg *_message;

lib/src/policy_engine.c

     /* Get a message object */
     union pd_msg *get_source_cap = chPoolAlloc(&pdb_msg_pool);
     /* Make a Get_Source_Cap message */
-    get_source_cap->hdr = PD_MSGTYPE_GET_SOURCE_CAP | PD_DATAROLE_UFP
-        | PD_SPECREV_2_0 | PD_POWERROLE_SINK | PD_NUMOBJ(0);
+    get_source_cap->hdr = cfg->pe.hdr_template | PD_MSGTYPE_GET_SOURCE_CAP
+        | PD_NUMOBJ(0);
     /* Transmit the Get_Source_Cap */
     chMBPost(&cfg->prl.tx_mailbox, (msg_t) get_source_cap, TIME_IMMEDIATE);
     chEvtSignal(cfg->prl.tx_thread, PDB_EVT_PRLTX_MSG_TX);
     /* Get a message object */
     union pd_msg *accept = chPoolAlloc(&pdb_msg_pool);
     /* Make an Accept message */
-    accept->hdr = PD_MSGTYPE_ACCEPT | PD_DATAROLE_UFP | PD_SPECREV_2_0
-        | PD_POWERROLE_SINK | PD_NUMOBJ(0);
+    accept->hdr = cfg->pe.hdr_template | PD_MSGTYPE_ACCEPT | PD_NUMOBJ(0);
     /* Transmit the Accept */
     chMBPost(&cfg->prl.tx_mailbox, (msg_t) accept, TIME_IMMEDIATE);
     chEvtSignal(cfg->prl.tx_thread, PDB_EVT_PRLTX_MSG_TX);
     /* Get a message object */
     union pd_msg *softrst = chPoolAlloc(&pdb_msg_pool);
     /* Make a Soft_Reset message */
-    softrst->hdr = PD_MSGTYPE_SOFT_RESET | PD_DATAROLE_UFP | PD_SPECREV_2_0
-        | PD_POWERROLE_SINK | PD_NUMOBJ(0);
+    softrst->hdr = cfg->pe.hdr_template | PD_MSGTYPE_SOFT_RESET | PD_NUMOBJ(0);
     /* Transmit the soft reset */
     chMBPost(&cfg->prl.tx_mailbox, (msg_t) softrst, TIME_IMMEDIATE);
     chEvtSignal(cfg->prl.tx_thread, PDB_EVT_PRLTX_MSG_TX);
     /* Get a message object */
     union pd_msg *reject = chPoolAlloc(&pdb_msg_pool);
     /* Make a Reject message */
-    reject->hdr = PD_MSGTYPE_REJECT | PD_DATAROLE_UFP | PD_SPECREV_2_0
-        | PD_POWERROLE_SINK | PD_NUMOBJ(0);
+    reject->hdr = cfg->pe.hdr_template | PD_MSGTYPE_REJECT | PD_NUMOBJ(0);
 
     /* Transmit the message */
     chMBPost(&cfg->prl.tx_mailbox, (msg_t) reject, TIME_IMMEDIATE);
     chMBObjectInit(&cfg->pe.mailbox, cfg->pe._mailbox_queue, PDB_MSG_POOL_SIZE);
     /* Initialize the old_tcc_match */
     cfg->pe._old_tcc_match = -1;
+    /* Initialize the PD message header template */
+    cfg->pe.hdr_template = PD_DATAROLE_UFP | PD_SPECREV_2_0 | PD_POWERROLE_SINK;
 
     while (true) {
         switch (state) {

src/device_policy_manager.c

             if (PD_PDO_SRC_FIXED_VOLTAGE_GET(capabilities, i) == scfg->v
                     && PD_PDO_SRC_FIXED_CURRENT_GET(capabilities, i) >= scfg->i) {
                 /* We got what we wanted, so build a request for that */
-                request->hdr = PD_MSGTYPE_REQUEST | PD_DATAROLE_UFP |
-                    PD_SPECREV_2_0 | PD_POWERROLE_SINK | PD_NUMOBJ(1);
+                request->hdr = cfg->pe.hdr_template | PD_MSGTYPE_REQUEST
+                    | PD_NUMOBJ(1);
                 if (scfg->flags & PDBS_CONFIG_FLAGS_GIVEBACK) {
                     /* GiveBack enabled */
                     request->obj[0] = PD_RDO_FV_MIN_CURRENT_SET(DPM_MIN_CURRENT)
         }
     }
     /* Nothing matched (or no configuration), so get 5 V at low current */
-    request->hdr = PD_MSGTYPE_REQUEST | PD_DATAROLE_UFP |
-        PD_SPECREV_2_0 | PD_POWERROLE_SINK | PD_NUMOBJ(1);
+    request->hdr = cfg->pe.hdr_template | PD_MSGTYPE_REQUEST | PD_NUMOBJ(1);
     request->obj[0] = PD_RDO_FV_MAX_CURRENT_SET(DPM_MIN_CURRENT)
         | PD_RDO_FV_CURRENT_SET(DPM_MIN_CURRENT)
         | PD_RDO_NO_USB_SUSPEND
     }
 
     /* Set the Sink_Capabilities message header */
-    cap->hdr = PD_MSGTYPE_SINK_CAPABILITIES | PD_DATAROLE_UFP | PD_SPECREV_2_0
-        | PD_POWERROLE_SINK | PD_NUMOBJ(numobj);
+    cap->hdr = cfg->pe.hdr_template | PD_MSGTYPE_SINK_CAPABILITIES
+        | PD_NUMOBJ(numobj);
 }
 
 bool pdbs_dpm_giveback_enabled(struct pdb_config *cfg)