media: video-i2c: support runtime PM

AMG88xx has a register for setting operating mode.  This adds support
runtime PM by changing the operating mode.

The instruction for changing sleep mode to normal mode is from the
reference specifications.

https://docid81hrs3j1.cloudfront.net/medialibrary/2017/11/PANA-S-A0002141979-1.pdf



Reviewed-by: Matt Ranostay <matt.ranostay@konsulko.com>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>