rockchip: rk3368: use common TPL board file

Use common tpl.c instead of rk3368-board-tpl.c

Signed-off-by: Kever Yang <kever.yang@rock-chips.com>
diff --git a/arch/arm/mach-rockchip/Kconfig b/arch/arm/mach-rockchip/Kconfig
index 8a7f2bb..3c17994 100644
--- a/arch/arm/mach-rockchip/Kconfig
+++ b/arch/arm/mach-rockchip/Kconfig
@@ -127,6 +127,7 @@
 	imply SPL_SEPARATE_BSS
 	imply SPL_SERIAL_SUPPORT
 	imply TPL_SERIAL_SUPPORT
+	imply TPL_ROCKCHIP_COMMON_BOARD
 	help
 	  The Rockchip RK3368 is a ARM-based SoC with a octa-core (organised
 	  into a big and little cluster with 4 cores each) Cortex-A53 including