Initiate magnetometer based compass calibration from button presses (#5553)

* Initiate magenetometer based compass calibration from button presses

- only active for BMX160 accelerometers on RAK_4631
- replace automatic calibration on power on with button triggered
  calibration
- set 5 presses to trigger 30s calibration
- set 6 presses to trigger 60s calibration (useful if unit is not
  handheld, ie vehicle mounted)
- show calibration time remaining on calibration alert screen

* Fix non RAK 4631 builds

- exclude changes from non RAK 4631 builds
- remove calls to screen when not present

* Fix build on RAK4631_eth_gw

- exclude all compass heading updates on variant without screen

---------

Co-authored-by: Ben Meadors <benmmeadors@gmail.com>

src/graphics/Screen.h

@@ -278,6 +278,10 @@ class Screen : public concurrency::OSThread
     bool hasHeading() { return hasCompass; }
 
     long getHeading() { return compassHeading; }
+
+    void setEndCalibration(uint32_t _endCalibrationAt) { endCalibrationAt = _endCalibrationAt; }
+    uint32_t getEndCalibration() { return endCalibrationAt; }
+
     // functions for display brightness
     void increaseBrightness();
     void decreaseBrightness();
@@ -673,6 +677,8 @@ class Screen : public concurrency::OSThread
 
     bool hasCompass = false;
     float compassHeading;
+    uint32_t endCalibrationAt;
+
     /// Holds state for debug information
     DebugInfo debugInfo;