rockchip: Kconfig: Enable SPL support for rk3568

Enable SPL support in Kconfig and add some related option in
rk3568_common.h

Signed-off-by: Nico Cheng <nico.cheng@rock-chips.com>
Signed-off-by: Jason Zhu <jason.zhu@rock-chips.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>
diff --git a/arch/arm/mach-rockchip/Kconfig b/arch/arm/mach-rockchip/Kconfig
index da6871e..d840c59 100644
--- a/arch/arm/mach-rockchip/Kconfig
+++ b/arch/arm/mach-rockchip/Kconfig
@@ -261,6 +261,8 @@
 config ROCKCHIP_RK3568
 	bool "Support Rockchip RK3568"
 	select ARM64
+	select SUPPORT_SPL
+	select SPL
 	select CLK
 	select PINCTRL
 	select RAM