video: sunxi: dw-hdmi: Read address from DT node

Currently HDMI controller MMIO address is hardcoded. Change that so
address is read from DT node. That will make adding support for new
variants a bit easier.

Signed-off-by: Jernej Skrabec <jernej.skrabec@gmail.com>
Signed-off-by: Samuel Holland <samuel@sholland.org>