drm/rockchip: cdn-dp: Load firmware if no monitor connected

If no monitor is connected, suspend/resume cycles result in firmware
load errors because the driver attempts to load the firmware while
the system is in suspend state. This results in a kernel warning and
traceback.

Loading the firmware during boot fixes the problem. Note that we can not
just call schedule_work conditionally in cdn_dp_pd_event() if the insertion
status changed. The problem would still be seen if a monitor is connected
for the first time during suspend.

Signed-off-by: Guenter Roeck <groeck@chromium.org>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Chris Zhong <zyw@rock-chips.com>