[media] vivid-tpg: move pattern-related fields to struct tpg_draw_params

Add a new function that fills in pattern-related fields in struct
tpg_draw_params.

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