drm/sun4i: Add compatible string for V3s display engine

Allwinner V3s features the new "Display Engine 2.0", which can now also
be driven with our subdrivers in sun4i-drm.

Add the compatible string for in sun4i_drv.c, in order to make the
display engine and its components probed.

Signed-off-by: Icenowy Zheng <icenowy@aosc.io>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>