sunxi: video: Give hotplug-detect (hpd) signal some time to show up

When using a hdmi powered hdmi to vga dongle, and cold booting a sunxi
device, the hpd detect code would not see the dongle (until a warm reboot),
because the dongle needs some time to boot.

So wait a bit (up to 200ms) for a hpd signal to show up before giving up.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>