drm/amd/display: Use periodic detection for ipx/headless

[WHY]
Hotplug is not detected in headless (no eDP) mode on dcn35x.
With no display dcn35x goes to IPS2 powersaving state where HPD interrupt
is not handled.

[HOW]
Use idle worker thread for periodic detection of HPD in headless mode.

Reviewed-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Cc: Mario Limonciello <mario.limonciello@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org
Signed-off-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Roman Li <roman.li@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.h

@@ -989,4 +989,7 @@ void *dm_allocate_gpu_mem(struct amdgpu_device *adev,
 						  enum dc_gpu_mem_alloc_type type,
 						  size_t size,
 						  long long *addr);
+
+bool amdgpu_dm_is_headless(struct amdgpu_device *adev);
+
 #endif /* __AMDGPU_DM_H__ */