media: intel/ipu6: add IPU6 buttress interface driver

The IPU6 buttress is the interface between IPU device (input system and
processing system) with rest of the SoC. It contains overall IPU hardware
control registers, these control registers are used as the interfaces with
the Intel Converged Security Engine and Punit to do firmware
authentication and power management.

Signed-off-by: Bingbu Cao <bingbu.cao@intel.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>