drm: rockchip: add reset controller dependency

When the reset controller subsystem is disabled, this driver
fails to build:

drivers/gpu/drm/rockchip/rockchip_drm_vop.c: In function 'vop_initial':
drivers/gpu/drm/rockchip/rockchip_drm_vop.c:1267:2: error: implicit declaration of function 'devm_reset_control_get' [-Werror=implicit-function-declaration]

The easiest solution is to add a dependency in Kconfig to avoid
that case.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Dave Airlie <airlied@gmail.com>

drivers/gpu/drm/rockchip/Kconfig

 config DRM_ROCKCHIP
 	tristate "DRM Support for Rockchip"
 	depends on DRM && ROCKCHIP_IOMMU
+	depends on RESET_CONTROLLER
 	select DRM_KMS_HELPER
 	select DRM_KMS_FB_HELPER
 	select DRM_PANEL