initial BMI270 support - NORMAL config file 8192 bytes

[nerdCopter]

• WIP
• Initial BMI270 support
• tested as flyable
• needs Configurator synchronization (Config wrongly shows 8k, 4k, etc. loops)
• intend to remove target definitions from this PR
• may need fixes
• NORMAL config file (8192 bytes)
• OSR4 mode is default

This code is ported mostly from Betaflight and minimally iNav. Thanks to project teams and GPL licensed opensource.
Intention of porting "CRT/IOC/CAS" from FlightNG/ATBetaflight if possible. Portability unknown at this time.
https://github.com/betaflight/betaflight/blob/master/LICENSE
https://github.com/iNavFlight/inav/blob/master/LICENSE
https://github.com/flightng/atbetaflight/blob/4.3-bsp-rebase/LICENSE

Massive thanks to @Peck07 for investigating and fixing some pre-existing failed works.
Massive thanks to @BeauBrewski for target definitions and help.

Closes #861

Further notes. @Peck07 said he made it work by picking BF's "pre-SPI" changes. So we need to verify if newer code exists to make bmi270 more efficient. Should also investigate @DusKing1's bmi270 updates from https://github.com/flightng/atbetaflight

Co-authored-by: KarateBrot [email protected]
Co-authored-by: Steve Evans [email protected]
Co-authored-by: chrisrosser [email protected]
Co-authored-by: Dominic Clifton [email protected]
Co-authored-by: mikeller [email protected]
Co-authored-by: Bruce Luckcuck [email protected]
Co-authored-by: Martin Luessi [email protected]
Co-authored-by: Peck07 [email protected]
Co-authored-by: nerdCopter [email protected]
Co-authored-by: Dusking1 [email protected]

[DusKing1]

I'll look into this once I got some spare time...

[nerdCopter]

BMI270_INT_EXTI is not a valid define.

• could add parameter at src/main/sensors/gyro.c:688 or use existing GYRO_1_EXTI_PIN or MPU_INT_EXTI

off-subject, same is true for non-existent ICM42688P_EXTI_PIN

[nerdCopter]

• found that mpu6000 drivers and defines are required for bm270i-only target to work.
• will need to rectify in firmware source-code.

[nerdCopter]

• defining USE_GYRO_EXTI (and USE_MPU_DATA_READY_SIGNAL) breaks linking stage.
• have not found a need for it yet, however. - needs investigation.

[nerdCopter]

Closing this in favor of FIFO. #930