Rename LITTLE_ENDIAN and BIG_ENDIAN defines

[Thannoy]

System-wide endian.h already defines both LITTLE_ENDIAN and BIG_ENDIAN as part of BSD compatibility.

Before this fix, since little endianess is always tested first, it is likely to be always selected even on big endian machines.

This commit adds "BMI160_" prefix to them in order to fix this name collision.

At least link below speak about this issue: https://bugs.launchpad.net/gcc-arm-embedded/+bug/1609078