drm/sun4i: Not all DW HDMI controllers has scrambled addresses

Currently supported Allwinner SoCs with DW HDMI controller have
scrambled addresses and read lock. However, that is not true in general.
For example, A80 and H6 have normal addresses and normal read access.

Move code for unscrambling addresses and unlocking read access to it's
own function and call it from init function.

Reviewed-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Jernej Skrabec <jernej.skrabec@siol.net>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181104182705.18047-16-jernej.skrabec@siol.net