drm/panfrost: Require the simple_ondemand governor

Panfrost depends on the simple_ondemand governor, and therefore
it's a required configuration. Select it.

Fixes: f3617b4 ("drm/panfrost: Select devfreq")
Signed-off-by: Ezequiel Garcia <ezequiel@collabora.com>
Reviewed-by: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20190605184859.9432-1-ezequiel@collabora.com

drivers/gpu/drm/panfrost/Kconfig

@@ -10,6 +10,7 @@ config DRM_PANFROST
 	select IOMMU_IO_PGTABLE_LPAE
 	select DRM_GEM_SHMEM_HELPER
 	select PM_DEVFREQ
+	select DEVFREQ_GOV_SIMPLE_ONDEMAND
 	help
 	  DRM driver for ARM Mali Midgard (T6xx, T7xx, T8xx) and
 	  Bifrost (G3x, G5x, G7x) GPUs.