AP_RPM: use millis/micros/panic functions

libraries/AP_RPM/AP_RPM.cpp

@@ -118,7 +118,7 @@ bool AP_RPM::healthy(uint8_t instance) const
         return false;
     }
     // assume we get readings at at least 1Hz
-    if (hal.scheduler->millis() - state[instance].last_reading_ms > 1000) {
+    if (AP_HAL::millis() - state[instance].last_reading_ms > 1000) {
         return false;
     }
     return true;

libraries/AP_RPM/RPM_PX4_PWM.cpp

@@ -92,7 +92,7 @@ void AP_RPM_PX4_PWM::update(void)
 
     if (count != 0) {
         state.rate_rpm = sum / count;
-        state.last_reading_ms = hal.scheduler->millis();
+        state.last_reading_ms = AP_HAL::millis();
     }
 }