rockchip: add common board file for U-Boot proper

Add common board file for Rockchip SoCs to avoid too much
copy-paste work for different SoCs.
This board file in charge for common board_init() and board_late_init()
in U-Boot proper.

Signed-off-by: Kever Yang <kever.yang@rock-chips.com>
diff --git a/arch/arm/mach-rockchip/Makefile b/arch/arm/mach-rockchip/Makefile
index 5cb2c6d..7d2a227 100644
--- a/arch/arm/mach-rockchip/Makefile
+++ b/arch/arm/mach-rockchip/Makefile
@@ -20,6 +20,7 @@
 # we can have the preprocessor correctly recognise both 0x0 and 0
 # meaning "turn it off".
 obj-y += boot_mode.o
+obj-$(CONFIG_ROCKCHIP_COMMON_BOARD) += board.o
 
 obj-$(CONFIG_ROCKCHIP_RK3188) += rk3188-board.o
 obj-$(CONFIG_ROCKCHIP_RK3128) += rk3128-board.o