[media] v4l: vsp1: Merge RPF and WPF pad ops structures

The two structures are identical, merge them and move the result to
vsp1_rwpf.c. All rwpf pad operations can now be declared static.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>