media: v4l2-tpg*.h: move headers to include/media/tpg and merge them

The v4l2-tpg*.h headers are meant to be used only internally by
vivid and vimc. There's no sense keeping them together with the
V4L2 kAPI headers. Also, one header includes the other as they're
meant to be used together. So, merge them.

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