drm/sun4i: Add if statement instead of depends on

drm/sun4i: Add if statement instead of depends on

The depends on relationship is obvious, and using an if statement will
propagate it to every option without the need for each and every one of
them to define it.

Reviewed-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>