Consolidation of issues about RM3100 compass

[and-sh]

Using the compass revealed the following problems:

1. Due to incorrect scaling most of compass data are lost
   magnetic field strength is about 0xEA6 lsb
   due to cancelling of low byte most of this data are lost.
   details Please, correct error in RM3100 compass measurement scaling #10746
2. Due to n.1 seems that no one use RM3100 compass with Inav. SPI is rarely accessible on most FC, so it is logical to change the bus to I2C and possible somebody will use it.
   details Change RM3100 defaulf bus to I2C #10747
3. The order or initializing registers is incorrect.
   details Please correct a small error in compass_rm3100.c #10748
4. A check new reading is unnecessary waste of time because sampling rate of compass is much more than reading rate.
   details Please, consider a tiny improvement to compass_rm3100.c #10752
5. Sampling rate can be substantially lower than default, used by Inav. This can lower the noise.
   details Please, consider a tiny improvement to compass_rm3100.c #10752

[b14ckyy]

Thanks a lot :)