drm: bridge: analogix/dp: move hpd detect to connector detect function

This change just make a little clean to make code more like
drm core expect, move hdp detect code from bridge->enable(),
and place them into connector->detect().

Note: Gustavo Padovan try to remove the controller and phy
power on function in bind time at bellow commit:
	drm/exynos: do not start enabling DP at bind() phase

But for now the connector status don't hardcode to connected,
need to operate dp phy in .detect function, so we need to revert
parts if Gustavo Padovan's changes, add phy poweron
function in bind time.

Tested-by: Caesar Wang <wxt@rock-chips.com>
Tested-by: Douglas Anderson <dianders@chromium.org>
Tested-by: Heiko Stuebner <heiko@sntech.de>
Tested-by: Javier Martinez Canillas <javier@osg.samsung.com>
Signed-off-by: Yakir Yang <ykk@rock-chips.com>