[media] v4l: vsp1: Add VIDIOC_EXPBUF support

Use the vb2 ioctl handler directly.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Tested-by: Jacopo Mondi <jacopo@jmondi.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>