sunxi: video: Set input sync enable

Add a write to the "unknown" (*) register to enable auto input sync, when
initially adding sunxi hdmi output support this magic write from the android
kernel code was missed, causing lcdc -> hdmi encoder sync problems.

With this write added, we can drop the modesetting retries and the extra
delays added to work around these sync problems.

With the retries dropped there also is no need to 0 all the enable flags at
the beginning of the modeset, as they are initialized to 0 already by
engines_init.

*) "unknown" is the actual name of this register in the android kernel sources

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Ian Campbell <ijc@hellion.org.uk>
Acked-by: Anatolij Gustschin <agust@denx.de>