drm/amdgpu: Check if SW SMU is supported before accessing funcs

smu.ppt_funcs is only initialized for ASICs supporting SW SMU.

On a Hawaii ASIC, attempting to access the udev attribute
ATTRS{power_dpm_state} will cause a null pointer deref in
amdgpu_get_dpm_state() because of this.

Fix by checking if SW SMU is supported first.
Signed-off-by: Leo Li <sunpeng.li@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Huang Rui <ray.huang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -144,7 +144,7 @@ static ssize_t amdgpu_get_dpm_state(struct device *dev,
 	struct amdgpu_device *adev = ddev->dev_private;
 	enum amd_pm_state_type pm;
 
-	if (adev->smu.ppt_funcs->get_current_power_state)
+	if (is_support_sw_smu(adev) && adev->smu.ppt_funcs->get_current_power_state)
 		pm = amdgpu_smu_get_current_power_state(adev);
 	else if (adev->powerplay.pp_funcs->get_current_power_state)
 		pm = amdgpu_dpm_get_current_power_state(adev);