[media] v4l: vsp1: Add HGT support

The HGT is a Histogram Generator Two-Dimensions. It computes a weighted
frequency histograms for hue and saturation areas over a configurable
region of the image with optional subsampling.

Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>