Reported by Nikolaus Schaller, Jan 27, 2019

iio has a feature called "mount-matrix" where the DT can 
specify a set of 9 strings which represent a rotation matrix.

An iio sensor driver can expose this to the /sys record so that 
user-space can read it and do its calculations.

For an example see:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/co
mmit/?h=v5.0-rc3&id=97eacb9166f4810368e180073dcbceeff0de34df

In kernel-iio drivers (like our iio-input-bridge) can access this 
property through iio_read_channel_ext_info()

So the task is to

1. add DT-Definitions for:
GTA04A3: BMA180, LIS302, HMC5840, ITG3200
GTA04A4: BMA180, HMC5840, ITG3200 (should be the same as GTA04A3)
GTA04A5: BMC150, BNO055
Pyra: BMC150, BNO055
GTA15: BMC150, BNO055
Udoo-Neo: Freescale drivers

2. add code to all affected drivers

3. make iio-input-bridge read this property and take it for 
(integer) calculations to generate input events