rockchip: rk3288: enable rockusb support on rk3288 based device

this patch enable rockusb support on rk3288 based device.

Signed-off-by: Eddie Cai <eddie.cai.linux@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/arm/mach-rockchip/Kconfig b/arch/arm/mach-rockchip/Kconfig
index 967290f..8510781 100644
--- a/arch/arm/mach-rockchip/Kconfig
+++ b/arch/arm/mach-rockchip/Kconfig
@@ -61,6 +61,8 @@
 	select SPL_BOARD_INIT if SPL
 	select SUPPORT_SPL
 	select SPL
+	imply USB_FUNCTION_ROCKUSB
+	imply CMD_ROCKUSB
 	help
 	  The Rockchip RK3288 is a ARM-based SoC with a quad-core Cortex-A17
 	  including NEON and GPU, 1MB L2 cache, Mali-T7 graphics, two