Add a helper to find timings based on the CEA-861 VIC code. Also,
add a helper that returns the pixel aspect ratio based on the
v4l2_dv_timings struct.

[mchehab@s-opensource.com: fix coding style]
Signed-off-by: NHans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: NMauro Carvalho Chehab <mchehab@s-opensource.com>