media: exynos-gsc: replace v4l2_crop by v4l2_selection

Replace the use of struct v4l2_crop by struct v4l2_selection.
Also drop the unused gsc_g_crop function.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Reviewed-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>