ipq40xx: add support for Compex WPJ428

ipq40xx: add support for Compex WPJ428

* QCA IPQ4028
* 256 MB of RAM
* 32 MB of SPI NOR flash (mx25l25635e)
* 128 MB of SPI NAND flash (gd5f1gq4ucy1g)
* 2T2R 2.4 GHz
  - QCA4019 hw1.0 (SoC)
  - uses AP-DK03 BDF from QCA4019/hw1.0/board-2.bin
* 2T2R 5 GHz
  - QCA4019 hw1.0 (SoC)
  - uses AP-DK03 BDF from QCA4019/hw1.0/board-2.bin
* 2 fully software controllable GPIO-LEDs
* 2 additional GPIO-LEDs which also affect the SIM card detection
* 1x button (reset)
* 1x GPIO buzzer
* 1x USB (xHCI)
* 1x NGFF (USB-only with Dual-SIM support, untested)
* TTL pins are on board (R124 is next to GND, then follows: RX, TX, VCC)
* 2x gigabit ethernet
  - phy@mdio4:
    + Manual: Ethernet port 0
    + gmac0 (ethaddr) in original firmware
    + 802.3af POE (HV version)
    + 24v passive POE (LV version)
  - phy@mdio3:
    + Manual: Ethernet port 1
    + gmac1 (eth1addr) in original firmware
* DC Jack connector
  + 24-56V (HV version)
  + 12-24V (LV version)

The SPI NAND flash isn't supported at the moment.

The bootloader has to be updated before OpenWrt is installed to fix a
reboot problem. The nor-ipq40xx-single.img from
https://downloads.compex.com.sg/?dir=uploads/QSDK/QCA-Reference/WPJ428/b170123-IPQ40xx-Reference-Firmware
has to be downloaded and the transfered in u-boot via TFTP

  set ipaddr 192.168.1.11
  set serverip 192.168.1.10
  ping ${serverip}
  tftpboot 0x84000000 nor-ipq40xx-single.img
  imgaddr=0x84000000 && source $imgaddr:script

The sysupgrade image can be installed directly on flash using u-boot:

  sf probe
  tftpboot 0x84000000 openwrt-ipq40xx-compex_wpj428-squashfs-sysupgrade.bin
  sf erase 0x00180000 +$filesize
  sf write 0x84000000 0x00180000 $filesize
  bootipq

The initramfs image can be started using

  tftpboot 0x82000000 openwrt-ipq40xx-compex_wpj428-initramfs-fit-uImage.itb
  set fdt_high 0x83000000
  bootm 0x82000000

The used SIM card slot can be changed using

  # slot 1 (also enables orange LED)
  echo 1 > /sys/class/gpio/gpio3/value
  # slot 2
  echo 0 > /sys/class/gpio/gpio3/value

It can be checked whether a SIM card is inserted in the current slot and
the red LED is subsequently on via:

  echo 2 > /sys/class/gpio/export
  cat /sys/class/gpio/gpio2/value

Signed-off-by: Sven Eckelmann <sven@narfation.org>