rockchip: board: Add minimal generic RK3566/RK3568 board

Add a minimal generic RK3566/RK3568 board that only have eMMC and SDMMC
enabled. This defconfig can be used to boot from eMMC or SD-card on most
RK3566/RK3568 boards that follow reference board design.

Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>
diff --git a/board/rockchip/evb_rk3568/MAINTAINERS b/board/rockchip/evb_rk3568/MAINTAINERS
index cc9eb43..fa8d119 100644
--- a/board/rockchip/evb_rk3568/MAINTAINERS
+++ b/board/rockchip/evb_rk3568/MAINTAINERS
@@ -7,6 +7,13 @@
 F:	arch/arm/dts/rk3568-evb-u-boot.dtsi
 F:	arch/arm/dts/rk3568-evb.dts
 
+GENERIC-RK3568
+M:	Jonas Karlman <jonas@kwiboo.se>
+S:	Maintained
+F:	configs/generic-rk3568_defconfig
+F:	arch/arm/dts/rk3568-generic.dts
+F:	arch/arm/dts/rk3568-generic-u-boot.dtsi
+
 LUBANCAT-2
 M:	Andy Yan <andyshrk@163.com>
 S:	Maintained