drm/bridge: analogix_dp: Don't use ANALOGIX_DP_PLL_CTL to control pll

There is no register named ANALOGIX_DP_PLL_CTL in Rockchip edp phy reg
list.  We should use BIT_4 in ANALOGIX_DP_PD to control the pll power
instead of ANALOGIX_DP_PLL_CTL.

Cc: Douglas Anderson <dianders@chromium.org>
Signed-off-by: zain wang <wzz@rock-chips.com>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Thierry Escande <thierry.escande@collabora.com>
Reviewed-by: Andrzej Hajda <a.hajda@samsung.com>
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
Reviewed-by: Archit Taneja <architt@codeaurora.org>
Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180423105003.9004-15-enric.balletbo@collabora.com