[media] v4l: sh_vou: Enable driver compilation with COMPILE_TEST

This helps increasing build testing coverage.

Cc: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Acked-by: Simon Horman <horms@verge.net.au>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>