drm/bridge: analogix_dp: Don't change psr while bridge is disabled

There is a race between AUX CH bring-up and enabling bridge which will
cause link training to fail. To avoid hitting it, don't change psr state
while enabling the bridge.

Cc: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Cc: Sean Paul <seanpaul@chromium.org>
Signed-off-by: zain wang <wzz@rock-chips.com>
Signed-off-by: Caesar Wang <wxt@rock-chips.com>
[seanpaul fixed up the commit message a bit and renamed *_supported to *_enabled]
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Thierry Escande <thierry.escande@collabora.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: Heiko Stuebner <heiko@sntech.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20180309222327.18689-4-enric.balletbo@collabora.com