Add BMI160 and external BMM150 support for hardware 2.1.0

[TobiasRoeddiger]

Summary

This adds sensor support for OpenEarable hardware revision 2.1.0, which replaces the integrated BMX160 with a standalone BMI160 and an external BMM150 magnetometer.

• Detect the standalone BMI160 at its alternate I2C address (0x69) during boot while retaining support for BMX160/BMI160 devices at 0x68.
• Configure the external BMM150 through the BMI160 auxiliary I2C interface.
• Decode the packed BMM150 samples correctly and apply the sensor factory-trim compensation.
• Preserve the compensated BMM150 axis order consistently across hardware revisions; paired multi-pose measurements show that hardware 2.1 must not receive a separate Y/Z inversion.
• Automatically report detected 2.1 hardware as at least 2.1.x when its stored revision is 2.0.x.
• Persist 2.1.0 when the UICR hardware-revision field is blank; use a runtime revision floor for programmed 2.0.x values because UICR cannot change those bits without erasing the page.

The changes are intentionally limited to IMU/magnetometer support and hardware-version detection; audio/ADAU behavior is unchanged. BMM150 factory compensation is distinct from unit-specific hard-/soft-iron calibration, so no prototype-specific magnetic offsets are hard-coded.

Validation

• Full firmware build succeeds for openearable_v2/nrf5340/cpuapp with nRF Connect SDK 3.0.1.
• The original hardware-support revision was flashed successfully to the hardware 2.1.0 prototype through J-Link and boot-time detection selected the BMI160 at 0x69.
• Captured eight stationary paired poses from a rigidly coupled hardware 2.0 BMX160 board and hardware 2.1 BMI160+BMM150 board, covering all six gravity directions plus yaw and a diagonal pose.
• Accelerometer comparison found no axis permutation or sign inversion; the fitted relative mounting angle was about 3.2 degrees.
• BMM150 factory-compensation output matches the Bosch-style reference calculation within 0.2 microtesla across the captured dataset, with stationary per-axis noise below about 1 microtesla.
• Paired magnetic changes show matching BMM150 axis direction between the two assemblies, invalidating the earlier hardware-2.1-only Y/Z inversion.

[github-actions]

Build output available:
openearable_v2_firmware.elf.zip
openearable_v2_fota.zip

[github-actions]

Build output available:
openearable_v2_firmware.elf.zip
openearable_v2_fota.zip