mvebu: add support for RIPE Atlas Probe v5

RIPE Atlas Probe v5 is a network measurement device based on Turris MOX.

u-boot bootscript supports booting both from the original Turris BTRFS
layout and default OpenWrt ext4 boot + root partition layout.

Specifications:
* SoC: Marvell ARMADA 3720
* RAM: 512 MiB, DDR3
* eMMC: 4G
* Ethernet: 1x 1GbE

MAC:
LAN MAC: label on board

Flash instructions:
* For using the default ext4 layout, boot into a live system using
tftpboot in u-boot and flash an OpenWrt SD image onto /dev/mmcblk0.
* For the Turris layout, put the new rootfs into subvolume '@', not
forgetting to add Image, device tree, and boot.scr to /boot.

Misc:
* USB connection is only for power. For UART access use the pin header:
  1: GND
  2: +1.8V
  5: TX
  6: RX
* Flashing the image onto Turris Shield won't work. Use Turris MOX image
  instead.

Signed-off-by: Tomáš Macholda <tomas.macholda@nic.cz>
Link: https://github.com/openwrt/openwrt/pull/20031
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>

package/boot/uboot-mvebu/Makefile

@@ -75,12 +75,20 @@ define U-Boot/rb5009
   UBOOT_IMAGE:=u-boot.elf
 endef
 
+define U-Boot/atlas
+  NAME:=RIPE Atlas Probe v5
+  BUILD_DEVICES:=ripe_atlas-v5
+  BUILD_SUBTARGET:=cortexa53
+  UBOOT_CONFIG:=turris_mox
+endef
+
 UBOOT_TARGETS:= \
 	mox \
 	clearfog \
 	helios4 \
 	omnia \
 	espressobin \
+	atlas \
 	uDPU \
 	eDPU \
 	rb5009