[media] v4l: vsp1: Add histogram support

The histogram common code will be used to implement support for both the
HGO and HGT histogram computation engines.

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