video: sunxi: Use DW-HDMI hpd function

It turns out that there are two ways how hot plug detection can be done.
One is standard way for DW HDMI controller - checking bit 2 in 0x3004
register. Another way is applicable only to Allwinner custom PHY - by
checking bit 19 in register 0x10038. Both methods are equally good as
far as we know.

Use standard method in order to reduce amount of custom code.

Reviewed-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Jernej Skrabec <jernej.skrabec@siol.net>
Signed-off-by: Andre Przywara <andre.przywara@arm.com>