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

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.

Testing has shown that this dongle needs 213ms to respond on a cold boot,
so wait up to 300ms for a hpd signal to show up before giving up.

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