[media] videodev2.h: add macros to map colorspace defaults

The mapping of COLORSPACE_DEFAULT, YCBCR_ENC_DEFAULT or QUANTIZATION_DEFAULT
to proper non-default values is fairly complex, and it is something that
needs to be done both in the kernel and in userspace.

So add macros that can do this conversion, making this available to both
kernel and userspace.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>