If the driver is in suspended mode, the dp block may be disabled, and
chip registers may not be accessible. Yet, the worker may be triggered
in this situation by an extcon event. If that happens, the following crash
will be seen.

cdn-dp fec00000.dp: [drm:cdn_dp_pd_event_work] *ERROR* Enable dp failed -19
cdn-dp fec00000.dp: [drm:cdn_dp_pd_event_work] Connected, not enabled. Enabling cdn
Bad mode in Error handler detected, code 0xbf000002 -- SError
CPU: 1 PID: 10357 Comm: kworker/1:2 Not tainted 4.4.21-05903-ge0514ea #1
Hardware name: Google Kevin (DT)
Workqueue: events cdn_dp_pd_event_work
task: ffffffc0cda67080 ti: ffffffc0b9b80000 task.ti: ffffffc0b9b80000
PC is at cdn_dp_clock_reset+0x30/0xa8
LR is at cdn_dp_enable+0x1e0/0x69c
...
Call trace:
[<ffffffc0005a7e24>] cdn_dp_pd_event_work+0x58/0x3f4
[<ffffffc0002397f0>] process_one_work+0x240/0x424
[<ffffffc00023a28c>] worker_thread+0x2fc/0x424
[<ffffffc00023f5fc>] kthread+0x10c/0x114
[<ffffffc000203dd0>] ret_from_fork+0x10/0x40

Problem is two-fold: The worker should not run while suspended, and the
suspend function should not call cdn_dp_disable() while the worker is
running.
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>