AP_HAL: allow motor poles to be recorded

enable ESC telemetry for SITL

libraries/AP_HAL/RCOutput.h

@@ -277,6 +277,10 @@ public:
       If not already done flush any dshot commands still pending
      */
     virtual bool prepare_for_arming() { return true; }
+    /*
+      set the number of motor poles to be used in rpm calculations
+     */
+    virtual void set_motor_poles(uint8_t poles) {}
 
     /*
       setup serial led output for a given channel number, with

libraries/AP_HAL/board/sitl.h

@@ -6,6 +6,7 @@
 #define HAL_OS_POSIX_IO 1
 #define HAL_OS_SOCKETS 1
 #define HAL_DSHOT_ALARM 0
+#define HAL_WITH_ESC_TELEM 1
 
 #define AP_FLASHSTORAGE_TYPE 3