ar71xx: add support for 8devices Rambutan development board

Rambutan is a Wifi module based on QCA9550/9557
http://www.8devices.com/products/rambutan

This commit adds basic support for Rambutan development kit

Specification:
- 720/600/200 MHz (CPU/DDR/AHB)
- 128 MB of DDR2 RAM
- 128 MB of NAND Flash
- 1x 100Mbps Ethernet
- 1x 1000Mbps Ethernet (PHY on dev-kit)
- 1x Wifi radio 2x2 MIMO, dualband 2.4 and 5 GHz
- 2x U.FL connectors on module, chip antennas on dev-kit
- 1x miniPCIe slot
- 1x USB2.0 host socket + 1x USB2.0 pins on 2.54mm header

Flash instructions:
Stock firmware is OpenWrt, so use:
 sysupgrade -n /tmp/lede-ar71xx-nand-rambutan-squashfs-sysupgrade.tar
or upgarde from GUI (don't save config)
Use factory image to flash from U-Boot:
 tftpboot 80060000 lede-ar71xx-nand-rambutan-squashfs-factory.ubi
 nand erase.part ubi
 nand write 80060000 ubi ${filesize}

Signed-off-by: Mantas Pucka <mantas@8devices.com>
[split support in uboot-envtools package into a separate commit,
fixed alphabetical order in lib/preinit/05_set_iface_mac_ar71xx]
Signed-off-by: Piotr Dymacz <pepe2k@gmail.com>

target/linux/ar71xx/base-files/lib/ar71xx.sh

@@ -811,6 +811,9 @@ ar71xx_board_detect() {
 	*"R6100")
 		name="r6100"
 		;;
+	*"Rambutan"*)
+		name="rambutan"
+		;;
 	*"RE450")
 		name="re450"
 		;;

target/linux/ar71xx/base-files/lib/preinit/05_set_iface_mac_ar71xx

@@ -44,6 +44,12 @@ preinit_set_mac_address() {
 			mac_wan=$(mtd_get_mac_binary caldata 6)
 			[ -n "$mac_wan" ] && ifconfig eth0 hw ether "$mac_wan"
 			;;
+		rambutan)
+			mac_lan=$(mtd_get_mac_binary art 0)
+			[ -n "$mac_lan" ] && ifconfig eth0 hw ether "$mac_lan"
+			mac_wan=$(mtd_get_mac_binary art 6)
+			[ -n "$mac_wan" ] && ifconfig eth1 hw ether "$mac_wan"
+			;;
 		tew-632brp)
 			fetch_mac_from_mtd config lan_mac wan_mac
 			;;

target/linux/ar71xx/base-files/lib/upgrade/platform.sh

@@ -521,6 +521,7 @@ platform_check_image() {
 	c-60|\
 	nbg6716|\
 	r6100|\
+	rambutan|\
 	wndr3700v4|\
 	wndr4300)
 		nand_do_platform_check $board $1
@@ -663,6 +664,7 @@ platform_pre_upgrade() {
 	c-60|\
 	nbg6716|\
 	r6100|\
+	rambutan|\
 	rb-411|\
 	rb-411u|\
 	rb-433|\