drm/amdgpu/display: clean up hdcp workqueue handling

Use the existence of the workqueue itself to determine when to
enable HDCP features rather than sprinkling asic checks all over
the code. Also add a check for the existence of the hdcp
workqueue in the irq handling on the off chance we get and HPD
RX interrupt with the CP bit set. This avoids a crash if
the driver doesn't support HDCP for a particular asic.

Fixes: 96a3b32e67236f ("drm/amd/display: only enable HDCP for DCN+")
Bug: https://bugzilla.kernel.org/show_bug.cgi?id=206519
Reviewed-by: Bhawanpreet Lakha <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>

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

···
 	mutex_lock(&aconnector->hpd_lock);
 
 #ifdef CONFIG_DRM_AMD_DC_HDCP
-	if (adev->asic_type >= CHIP_RAVEN)
+	if (adev->dm.hdcp_workqueue)
 		hdcp_reset_display(adev->dm.hdcp_workqueue, aconnector->dc_link->link_index);
 #endif
 	if (aconnector->fake_enable)
···
 		}
 	}
 #ifdef CONFIG_DRM_AMD_DC_HDCP
-	if (hpd_irq_data.bytes.device_service_irq.bits.CP_IRQ)
-		hdcp_handle_cpirq(adev->dm.hdcp_workqueue,  aconnector->base.index);
+	    if (hpd_irq_data.bytes.device_service_irq.bits.CP_IRQ) {
+		    if (adev->dm.hdcp_workqueue)
+			    hdcp_handle_cpirq(adev->dm.hdcp_workqueue,  aconnector->base.index);
+	    }
 #endif
 	if ((dc_link->cur_link_settings.lane_count != LANE_COUNT_UNKNOWN) ||
 	    (dc_link->type == dc_connection_mst_branch))
···
 		drm_connector_attach_vrr_capable_property(
 			&aconnector->base);
 #ifdef CONFIG_DRM_AMD_DC_HDCP
-		if (adev->asic_type >= CHIP_RAVEN)
+		if (adev->dm.hdcp_workqueue)
 			drm_connector_attach_content_protection_property(&aconnector->base, true);
 #endif
 	}