media: atomisp: report the visible resolution

The atomisp sensors and logic adds an extra pad lines/columns,
called "dvs envelope". It also uses an extra 12 lines/columns
at the sensor for BYT.

As those are not visible to userspace, the V4L2 API should
decrement such values when reporting the current resolution.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>