[media] videodev2.h Add HSV encoding

Some hardware maps the Hue between 0 and 255 instead of 0-179. Support
this format with a new field hsv_enc.

Signed-off-by: Ricardo Ribalda Delgado <ricardo.ribalda@gmail.com>
Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>