drm/sun4i: virtual CMA addresses are not needed

Driver never uses virtual address of DRM CMA buffers. Switch to CMA
helpers which don't deal with virtual mapping.

This was actually already the case before commit ad408c76
("drm/sun4i: Use DRM_GEM_CMA_VMAP_DRIVER_OPS for GEM operations"),
but only convenient macro at the time used helpers with virtual
mapping.

Signed-off-by: Jernej Skrabec <jernej.skrabec@gmail.com>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://patchwork.freedesktop.org/patch/msgid/20211019181028.4190737-1-jernej.skrabec@gmail.com