ath79: add support for Atheros DB120 reference board

ath79: add support for Atheros DB120 reference board

Atheros DB120 reference board.

Specifications:

SoC:    QCA9344
DRAM:   128Mb DDR2
Flash:  8Mb SPI-NOR, 128Mb NAND flash
Switch: 5x 10/100Mbps via AR8229 switch (integrated into SoC),
        5x 10/100/1000Mbps via QCA8237 via RGMII
WLAN:   AR9300 (SoC, 2.4G+5G) + AR9340 (PCIe, 5G-only)
USB:    1x 2.0
UART:   standard QCA UART header
JTAG:   yes
Button: 1x reset
LEDs:   a lot
Slots:  2x mPCIe + 1x mini-PCI, but using them requires
        additional undocumented changes.
Misc:   The board allows to boot off NAND, and there is
        I2S audio support as well - also requiring
        additional undocumented changes.

Installation:

1. Original bootloader

   Connect the board to ethernet
   Set up a server with an IP address of 192.168.1.10
   Make the openwrt-ath79-generic-atheros_db120-squashfs-factory.bin
   available via TFTP

   tftpboot 0x80060000 openwrt-ath79-generic-atheros_db120-squashfs-factory.bin
   erase 0x9f050000 +$filesize
   cp.b $fileaddr 0x9f050000 $filesize

2. pepe2k's u-boot_mod

   Connect the board to ethernet
   Set up a server with an IP address of 192.168.1.10
   Make the openwrt-ath79-generic-atheros_db120-squashfs-factory.bin
   available via TFTP, as "firmware.bin"

   run fw_upg

   Reboot the board.

Signed-off-by: Zoltan HERPAI <wigyori@uid0.hu>
[explicit factory recipe in generic.mk, sorting in 10-ath9k-eeprom,
 convert to nvmem, use fwconcat* names in DTS, remove unneeded DT
 labels, remove redundant uart node]
Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>