Similar to commit 26db46bc ("drm/bridge: parade-ps8640: Ensure bridge
is suspended in .post_disable()"). Add a mutex to ensure that aux transfer
won't race with atomic_disable by holding the PM reference and prevent
the bridge from suspend.

Also we need to use pm_runtime_put_sync_suspend() to suspend the bridge
instead of idle with pm_runtime_put_sync().

Fixes: 3203e497 ("drm/bridge: anx7625: Synchronously run runtime suspend.")
Fixes: adca62ec ("drm/bridge: anx7625: Support reading edid through aux channel")
Signed-off-by: Hsin-Yi Wang <hsinyi@chromium.org>
Tested-by: Xuxin Xiong <xuxinxiong@huaqin.corp-partner.google.com>
Reviewed-by: Pin-yen Lin <treapking@chromium.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240118015916.2296741-1-hsinyi@chromium.org