V4L/DVB (12625): Add new V4L2_FMT_FLAG_EMULATED flag to videodev2.h

V4L2_FMT_FLAG_EMULATED	0x0002	This format is not native to the device but
emulated through software (usually libv4l2), where possible try to use a
native format instead for better performance.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>