ath79: add support for Compex WPJ558 (16M)

Specifications:
- SoC: QCA9558
- DRAM: 128MB DDR2
- Flash: 16MB SPI-NOR
- Wireless: on-board abgn 2×2 2.4GHz radio
- Ethernet: 2x 10/100/1000 Mbps (1x 802.11af PoE)
- miniPCIe slot

Flash instruction:
- From u-boot

tftpboot 0x80500000 openwrt-ath79-generic-compex_wpj558-16m-squashfs-sysupgrade.bin
erase 0x9f030000 +$filesize
cp.b $fileaddr 0x9f030000 $filesize
boot

- From cpximg loader

The cpximg loader can be started either by holding the reset button
during power up. Once it's running, a TFTP-server under 192.168.1.1 will accept
the image appropriate for the board revision that is etched on the board.

For example, if the board is labelled '6A07':

tftp -v -m binary 192.168.1.1 -c put openwrt-ath79-generic-compex_wpj558-16m-squashfs-cpximg-6a07.bin

Signed-off-by: Romain Mahoux <romain@mahoux.fr>
[convert to nvmem, remove redundant lan_mac in 02_network]
Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>

target/linux/ath79/generic/base-files/etc/board.d/02_network

@@ -221,6 +221,10 @@ ath79_setup_interfaces()
 		ucidef_add_switch "switch0" \
 			"0@eth0" "3:lan" "2:wan"
 		;;
+	compex,wpj558-16m)
+		ucidef_add_switch "switch0" \
+			"1:wan" "5:lan" "6@eth0"
+		;;
 	devolo,dlan-pro-1200plus-ac|\
 	devolo,magic-2-wifi)
 		ucidef_add_switch "switch0" \
@@ -528,6 +532,7 @@ ath79_setup_macs()
 		wan_mac=$(macaddr_add $(mtd_get_mac_binary art 0x0) 1)
 		;;
 	compex,wpj344-16m|\
+	compex,wpj558-16m|\
 	compex,wpj563)
 		wan_mac=$(mtd_get_mac_binary u-boot 0x2e018)
 		;;