sunxi: add support for Beelink X2

Specifications:
- SoC: Allwinner H3 Quad Cortex-A7 1.2GHz
- Flash: 8GB eMMC
- RAM: 1GB DDR3
- Ethernet: 1x100M
- Wifi: RTL8189FTV or AP6181
- 1x USB-A Host
- 1x USB-A Host/Device
- 2x Button
- 2x LED
- HDMI, SPDIF, IR

Install by following standard SD card flashing instructions.
Image can also be flashed to eMMC.

Signed-off-by: Kyle Hendry <kylehendrydev@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/18732
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>

package/boot/uboot-sunxi/Makefile

@@ -92,6 +92,12 @@ define U-Boot/Bananapro
   BUILD_DEVICES:=lemaker_bananapro
 endef
 
+define U-Boot/beelink_x2
+  BUILD_SUBTARGET:=cortexa7
+  NAME:=Beelink X2 (H3)
+  BUILD_DEVICES:=roofull_beelink-x2
+endef
+
 define U-Boot/Cubieboard
   BUILD_SUBTARGET:=cortexa8
   NAME:=Cubieboard
@@ -388,6 +394,7 @@ UBOOT_TARGETS := \
 	bananapi_p2_zero \
 	Bananapi_M2_Ultra \
 	Bananapro \
+	beelink_x2 \
 	Cubieboard \
 	Cubieboard2 \
 	Cubietruck \