ath79: add support for jjPlus JWAP230

ath79: add support for jjPlus JWAP230

The jjPlus JWAP230 is an access point board built around the QCA9558,
with built-in 2.4GHz 3x3 N WiFi (28dBm). It can be expanded with 2
mini-PCIe boards, and has an USB2 root port.

Specifications:
- SOC: Qualcomm Atheros QCA9558
- CPU: 720MHz
- H/W switch: QCA8327 rev 2
- Flash: 16 MiB SPI NOR (en25qh128)
- RAM: 128 MiB DDR2
- WLAN: AR9550 built-in SoC bgn 3T3R (ath9k)
- PCI: 2x mini-PCIe (optional 5V)
- LEDs: 6x LEDs (3 are currently available)
- Button: 1x Reset (not yet defined)
- USB2:
  - 1x Type A root port
  - 1x combined mini-PCIe
- Ethernet:
  - 2x 10/100/1000 (1x PoE 802.3af (36-57 V))

Notes:
 The device used to be supported in the ar71xx target.
 For upgrades: Please use "sysupgrade --force -n <image>".
 This will restore the device back to OpenWrt defaults!

MAC address assignment:
    use   source
    LAN   art 0x0
    WAN   art 0x6
    WLAN  art 0x1002 (as part of the calibration data)

Flash instructions:
- install from u-boot with tftp (requires serial access)
  > setenv ipaddr a.b.c.d
  > setenv serverip e.f.g.h
  > tftp 0x80060000 \
      openwrt-ath79-generic-jjplus_jwap230-squashfs-sysupgrade.bin
  > erase 0x9f050000 +${filesize}
  > cp.b $fileaddr 0x9f050000 $filesize
  > setenv bootcmd bootm 0x9f050000
  > saveenv

Signed-off-by: Olivier Valentin <valentio@free.fr>
[Added DT-Leds (based on ar71xx), Added more notes about sysupgrade,
fixed "qca9550" to match SoC in commit and dts file name]
Signed-off-by: Christian Lamparter <chunkeey@gmail.com>