Some edp screen do not have hpd signal, so we can't just return
failed when hpd plug in detect failed.

This is an hardware property, so we need add a devicetree property
"analogix,need-force-hpd" to indicate this sutiation.
Acked-by: NRob Herring <robh@kernel.org>
Tested-by: NCaesar Wang <wxt@rock-chips.com>
Tested-by: NDouglas Anderson <dianders@chromium.org>
Tested-by: NHeiko Stuebner <heiko@sntech.de>
Tested-by: NJavier Martinez Canillas <javier@osg.samsung.com>
Signed-off-by: NYakir Yang <ykk@rock-chips.com>