media: atmel: atmel-isi: add support for mono sensors, GRAY and Y16

This adds support for GREY and Y16 formats, based on Y10 mbus codes.
Y16 needs to go through preview path in the ISI, with 2 pixels per word,
and it fits the Y16 format. The ISI data lines need to be MSB aligned with
the sensor data lines.
GREY format in 8 bits per pixel is done by dropping the 2 LSB bits
from the Y10 format, and packed as 4 pixels per word.

Suggested-by: Wenyou Yang <wenyou.yang@microchip.com>
Signed-off-by: Eugen Hristev <eugen.hristev@microchip.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>