drm/sun4i: Rework DE2 register defines

drm/sun4i: Rework DE2 register defines

Most, if not all, registers found in DE2 still exists in DE3. However,
units are on different base addresses.

To prepare for addition of DE3 support, registers macros are reworked so
they take base address as parameter.

Signed-off-by: Jernej Skrabec <jernej.skrabec@siol.net>
[rebased]
Signed-off-by: Icenowy Zheng <icenowy@aosc.io>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181104182705.18047-10-jernej.skrabec@siol.net