Currently this driver does not support cropping. The supported modes
are the following, all capturing the entire area:

 - 3840x2160, 1:1 binning (native sensor resolution)
 - 1920x1080, 2:1 binning
 - 1280x720,  3:1 binning

The VIDIOC_SUBDEV_S_FMT ioctl chooses among these 3 configurations the
one that matches the requested format.

Add cropping support via VIDIOC_SUBDEV_S_SELECTION: with target
V4L2_SEL_TGT_CROP to choose the captured area, with
V4L2_SEL_TGT_COMPOSE to choose the output resolution.

To maintain backward compatibility we also allow setting the compose
format via VIDIOC_SUBDEV_S_FMT. To obtain this, compose rect and
output format are computed in the common helper function
__imx274_change_compose(), which sets both to the same width/height
values.

Cropping also calls __imx274_change_compose() whenever cropping rect
size changes in order to reset the compose rect (and output format
size) for 1:1 binning.

Also rename enum imx274_mode to imx274_binning (and its values from
IMX274_MODE_BINNING_* to IMX274_BINNING_*). Without cropping, the two
naming are equivalent. With cropping, the resolution could be
different, e.g. using 2:1 binning mode to crop 1200x960 and output a
600x480 format. Using binning in the names avoids any
misunderstanding. For the same reason, replace the 'size' field in
struct imx274_frmfmt with 'bin_ratio'.

[Sakari Ailus: Remove leftover condition in imx274_apply_trimming]
Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>