Partially implement vrange requests

Requests for fixed voltages are now made from the voltage range.  This
isn't a terrible behavior, but I might want to be able to make requests
from programmable supplies from the range as well.  'Twould be more
complicated though, and provide comparitively little benefit.  I'll
think about it, and maybe put out a request for comments.

src/device_policy_manager.c

@@ -117,6 +117,41 @@ bool pdbs_dpm_evaluate_capability(struct pdb_config *cfg,
                 /* Update requested voltage */
                 dpm_data->_requested_voltage = PD_PRV2MV(PD_MV2PRV(scfg->v));
 
+                dpm_data->_capability_match = true;
+                return true;
+            }
+        }
+        /* Look at the PDOs a second time to see if one falls in our voltage
+         * range. */
+        for (uint8_t i = 0; i < numobj; i++) {
+            /* If we have a fixed PDO, its V equals our desired V, and its I is
+             * at least our desired I */
+            if ((capabilities->obj[i] & PD_PDO_TYPE) == PD_PDO_TYPE_FIXED
+                    && PD_PDO_SRC_FIXED_CURRENT_GET(capabilities, i) >= scfg->i
+                    && PD_PDO_SRC_FIXED_VOLTAGE_GET(capabilities, i) >= PD_MV2PDV(scfg->vmin)
+                    && PD_PDO_SRC_FIXED_VOLTAGE_GET(capabilities, i) <= PD_MV2PDV(scfg->vmax)) {
+                /* We got what we wanted, so build a request for that */
+                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)
+                        | PD_RDO_FV_CURRENT_SET(scfg->i)
+                        | PD_RDO_NO_USB_SUSPEND | PD_RDO_GIVEBACK
+                        | PD_RDO_OBJPOS_SET(i + 1);
+                } else {
+                    /* GiveBack disabled */
+                    request->obj[0] = PD_RDO_FV_MAX_CURRENT_SET(scfg->i)
+                        | PD_RDO_FV_CURRENT_SET(scfg->i)
+                        | PD_RDO_NO_USB_SUSPEND | PD_RDO_OBJPOS_SET(i + 1);
+                }
+                if (dpm_data->usb_comms) {
+                    request->obj[0] |= PD_RDO_USB_COMMS;
+                }
+
+                /* Update requested voltage */
+                dpm_data->_requested_voltage = PD_PDV2MV(PD_PDO_SRC_FIXED_VOLTAGE_GET(capabilities, i));
+
                 dpm_data->_capability_match = true;
                 return true;
             }