drm/amdgpu: move poll enabled/disable into non DC path

Some amd asics having reliable hotplug support don't call
drm_kms_helper_poll_init in driver init sequence. However,
due to the unified suspend/resume path for all asics, because
the output_poll_work->func is not set for these asics, a warning
arrives when suspending.

[   90.656049]  <TASK>
[   90.656050]  ? console_unlock+0x4d/0x100
[   90.656053]  ? __irq_work_queue_local+0x27/0x60
[   90.656056]  ? irq_work_queue+0x2b/0x50
[   90.656057]  ? __wake_up_klogd+0x40/0x60
[   90.656059]  __cancel_work_timer+0xed/0x180
[   90.656061]  drm_kms_helper_poll_disable.cold+0x1f/0x2c [drm_kms_helper]
[   90.656072]  amdgpu_device_suspend+0x81/0x170 [amdgpu]
[   90.656180]  amdgpu_pmops_runtime_suspend+0xb5/0x1b0 [amdgpu]
[   90.656269]  pci_pm_runtime_suspend+0x61/0x1b0

drm_kms_helper_poll_enable/disable is valid when poll_init is called in
amdgpu code, which is only used in non DC path. So move such codes into
non-DC path code to get rid of such warnings.

v1: introduce use_kms_poll flag in amdgpu as the poll stuff check
v2: use dc_enabled as the flag to simply code
v3: move code into non DC path instead of relying on any flag

Bug: drm/amd#2411


Fixes: a4e77172 ("drm/probe_helper: sort out poll_running vs poll_enabled")
Reported-by: Bert Karwatzki <spasswolf@web.de>
Suggested-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Suggested-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Guchun Chen <guchun.chen@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>