media: v4l2: Documentation of HEVC compressed format

Add V4L2 definition for HEVC compressed format which is also
known as H.265.

Signed-off-by: Smitha T Murthy <smitha.t@samsung.com>
Reviewed-by: Andrzej Hajda <a.hajda@samsung.com>
Reviewed-by: Stanimir Varbanov <stanimir.varbanov@linaro.org>
Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>