[media] media: davinci: vpif_display: use SIMPLE_DEV_PM_OPS

this patch uses SIMPLE_DEV_PM_OPS, and drops unneeded members
from io_usrs, usrs and makes use of vb2 helepers instead.

Signed-off-by: Lad, Prabhakar <prabhakar.csengg@gmail.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>