media: stm32-dcmi: g_/s_selection crop support

Implements g_/s_selection crop support by using DCMI crop
hardware feature.
User can first get the maximum supported resolution of the sensor
by calling g_selection(V4L2_SEL_TGT_CROP_BOUNDS).
Then user call to s_selection(V4L2_SEL_TGT_CROP) will reset sensor
to its maximum resolution and crop request is saved for later usage
in s_fmt().
Next call to s_fmt() will check if sensor can do frame size request
with crop request. If sensor supports only discrete frame sizes,
the frame size which is larger than user request is selected in
order to be able to match the crop request. Then s_fmt() resolution
user request is adjusted to match crop request resolution.
Signed-off-by: Hugues Fruchet <hugues.fruchet@st.com>
Signed-off-by: Hans Verkuil <hansverk@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>