media: vsp1: Remove artificial minimum width/height limitation

The VSP1 has a minimum width and height of a single pixel, with the
exception of pixel formats with sub-sampling.

Remove the artificial minimum width and minimum height limitation, and
instead clamp the minimum dimensions based upon the sub-sampling
parameter of that dimension.

Signed-off-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>