media: v4l2-tpg.h: rename color structs

The color structs right now are just "color" and "color16".
That may lead into conflicts, and don't define precisely what
they meant. As those are used by two drivers (vivid and vimc),
this is even on a somewhat public header!

So rename them to:
	color ->  tpg_rbg_color8
	color16 ->  tpg_rbg_color16

Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>