ramips: add support for Ubiquiti EdgeRouter X-SFP

This patch adds support for the Ubiquiti EdgeRouter X-SFP and
improves support for the EdgeRouter X (PoE-passthrough).

Specification:
- SoC: MediaTek MT7621AT
- Flash: 256 MiB
- RAM: 265 MiB
- Ethernet: 5 x LAN (1000 Mbps)
- UART: 1 x UART on PCB (3.3V, RX, TX, GND) - 57600 8N1
- EdgeRouter X:
  - 1 x PoE-Passtrough (Eth4)
  - powered by Wallwart or passive PoE
- EdgeRouter X-SFP:
  - 5 x PoE-Out (24V, passive)
  - 1 x SFP (unknown status)
  - powered by Wallwart (24V)

Doesn't work:
* SoC has crypto engine but no open driver.
* SoC has nat acceleration, but no open driver.
* This router has 2MB spi flash soldered in but MT
  nand/spi drivers do not support pin sharing,
  so it is not accessable and disabled. Stock
  firmware could read it and it was empty.

Installation

via vendor firmware:
- build an Initrd-image (> 3MiB) and upload the factory-image
- initrd can have luci-mod-failsafe
- flash final firmware via LuCI / sysupgrade on rebooted system

via TFTP:
- stop uboot into tftp-load into option "1"
- upload factory.bin image

Signed-off-by: Sven Roederer <devel-sven@geroedel.de>

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

@@ -252,7 +252,8 @@ platform_check_image() {
 		# these boards use metadata images
 		return 0
 		;;
-	ubnt-erx)
+	ubnt-erx|\
+	ubnt-erx-sfp)
 		nand_do_platform_check "$board" "$1"
 		return $?;
 		;;
@@ -274,7 +275,8 @@ platform_nand_pre_upgrade() {
 	local board=$(ramips_board_name)
 
 	case "$board" in
-	ubnt-erx)
+	ubnt-erx|\
+	ubnt-erx-sfp)
 		platform_upgrade_ubnt_erx "$ARGV"
 		;;
 	esac
@@ -286,7 +288,8 @@ platform_do_upgrade() {
 	case "$board" in
 	hc5962|\
 	r6220|\
-    	ubnt-erx)
+	ubnt-erx|\
+	ubnt-erx-sfp)
 		nand_do_upgrade "$ARGV"
 		;;
 	*)