media: atmel: atmel-isc-base: allow 8 bit direct dump

In case the format that the sensor sends is 8 bit only (like GREY for
example) we need to be able to bypass ISC pipeline and directly dump
8 bits.
That's why the hardcoded value of 16 bpp is not correct in all cases.
This change allows the output format to decide what is the correct bpp
(bits per pixel) such that the result is in the proper format.

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>