[media] m5mols: Add exposure metering control

This patch adds V4L2_CID_EXPOSURE_METERING control which allows
to select the light metering mode for automatic exposure as one
of the following modes: spot (small area at the frame center),
center weighted and frame averaged.

Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>