media: camss: add support for vidioc_enum_framesizes ioctl

VIDIOC_ENUM_FRAMESIZES support in the video capture driver is required by
libcamera. Without this change libcamera errors out with:
"ERROR V4L2 v4l2_videodevice.cpp:1059 /dev/video0[cap]: Unable to enumerate
frame sizes: Inappropriate ioctl for device"

Signed-off-by: Andrey Konovalov <andrey.konovalov@linaro.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>