media: ti-vpe: cal: Add pixel processing context

CAL has 4 pixel processing contexts (PIX PROC) of which the driver
currently uses pix proc 0 for PHY0, and pix proc 1 for PHY1 (as the
driver supports only a single source per PHY).

Add a pix_proc field to cal_ctx to allow us to use different pix proc
contexts in the future

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>