amdgpu/pm: set pp_dpm_dcefclk to readonly on NAVI10 and newer gpus

v2 : change condition to apply to all chips after NAVI10

Writing to dcefclk causes the gpu to become unresponsive, and requires a reboot.
Patch prevents user from successfully writing to file pp_dpm_dcefclk on parts
NAVI10 and newer, and gives better user feedback that this operation is not allowed.
Signed-off-by: Darren Powell <darren.powell@amd.com>
Reviewed-by: Kenneth Feng <kenneth.feng@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/pm/amdgpu_pm.c

@@ -1893,6 +1893,14 @@ static int default_attr_update(struct amdgpu_device *adev, struct amdgpu_device_
 		}
 	}
 
+	if (DEVICE_ATTR_IS(pp_dpm_dcefclk)) {
+		/* SMU MP1 does not support dcefclk level setting */
+		if (asic_type >= CHIP_NAVI10) {
+			dev_attr->attr.mode &= ~S_IWUGO;
+			dev_attr->store = NULL;
+		}
+	}
+
 #undef DEVICE_ATTR_IS
 
 	return 0;