ARM: rockchip: rv1108: Add a board_usb_init for USB OTG

Like it is done for other Rockchip SoCs, introduce a board_usb_init()
function so that USB OTG can be functional on rv1108 too.

Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>
Reviewed-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
diff --git a/arch/arm/mach-rockchip/Makefile b/arch/arm/mach-rockchip/Makefile
index 05706c4..368302e 100644
--- a/arch/arm/mach-rockchip/Makefile
+++ b/arch/arm/mach-rockchip/Makefile
@@ -33,6 +33,7 @@
 obj-$(CONFIG_ROCKCHIP_RK3288) += rk3288-board.o
 obj-$(CONFIG_ROCKCHIP_RK3036) += rk3036-board.o
 obj-$(CONFIG_ROCKCHIP_RK3399) += rk3399-board.o
+obj-$(CONFIG_ROCKCHIP_RV1108) += rv1108-board.o
 endif
 
 obj-$(CONFIG_$(SPL_TPL_)RAM) += sdram_common.o