[media] v4l: vsp1: Fix tri-planar format support through DRM API

The vsp1 driver supports tri-planar formats, but the DRM API only passes
two memory addresses. Add a third one.

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