drm: Switch to use DEVFREQ_GOV_SIMPLE_ONDEMAND constant

Since governor name is defined by DEVFREQ framework internally, use the
macro definition instead of using the name directly.
Signed-off-by: Yue Hu <huyue2@yulong.com>
Reviewed-by: Chanwoo Choi <cw00.choi@samsung.com>
Acked-by: Jordan Crouse <jcrouse@codeaurora.org> for the msm part.
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20190725035239.1192-1-zbestahu@gmail.com

drivers/gpu/drm/msm/msm_gpu.c

@@ -95,7 +95,8 @@ static void msm_devfreq_init(struct msm_gpu *gpu)
 	 */
 
 	gpu->devfreq.devfreq = devm_devfreq_add_device(&gpu->pdev->dev,
-			&msm_devfreq_profile, "simple_ondemand", NULL);
+			&msm_devfreq_profile, DEVFREQ_GOV_SIMPLE_ONDEMAND,
+			NULL);
 
 	if (IS_ERR(gpu->devfreq.devfreq)) {
 		DRM_DEV_ERROR(&gpu->pdev->dev, "Couldn't initialize GPU devfreq\n");

drivers/gpu/drm/panfrost/panfrost_devfreq.c

@@ -157,7 +157,8 @@ int panfrost_devfreq_init(struct panfrost_device *pfdev)
 	dev_pm_opp_put(opp);
 
 	pfdev->devfreq.devfreq = devm_devfreq_add_device(&pfdev->pdev->dev,
-			&panfrost_devfreq_profile, "simple_ondemand", NULL);
+			&panfrost_devfreq_profile, DEVFREQ_GOV_SIMPLE_ONDEMAND,
+			NULL);
 	if (IS_ERR(pfdev->devfreq.devfreq)) {
 		DRM_DEV_ERROR(&pfdev->pdev->dev, "Couldn't initialize GPU devfreq\n");
 		ret = PTR_ERR(pfdev->devfreq.devfreq);