drm/panfrost: Require the simple_ondemand governor

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

Fixes: f3617b449d0b ("drm/panfrost: Select devfreq")
Signed-off-by: Ezequiel Garcia <[e-mail]>
Reviewed-by: Tomeu Vizoso <[e-mail]>
Signed-off-by: Rob Herring <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/gpu/drm/panfrost/Kconfig

···
 	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.