Fixed some review findings
Unified dshot average rpm calculations into one single function
Renamed calcEscRpm to erpmToRpm, and moved function to dshot.c
Removed unused esc_sensor.h header file from dshot.c
Removed esc_sensor.h header from modules that no longer needs it
Average RPM calculated by demmand only when rpm data is updated
Renamed rpm to averageRpm and fixed a bug
Update average rpm when telemetry data is received
Removed blank line
Fixed review findings
Fixed return values for erpmToRpm and getDshotAverageRpm so rpm value doesn't truncate
Restored osd_esc_rmp_alarm setting. This setting is used to set an alarm to notify when rpm goes down a specified threshold. Rpm can go over 109krpm (1s 26kv motors setup), but a low rpm alarm doesn't have to be set to a so high value so at this time [0-32767] seems an acceptable range
Rebased to master
The calculated combined ESC sensor data could potentially overflow in some extreme cases and the problem would be more likely in cases with more than 4 motors.
