ipq40xx: add support for Plasma Cloud PA1200

ipq40xx: add support for Plasma Cloud PA1200

Device specifications:

* QCA IPQ4018
* 256 MB of RAM
* 32 MB of SPI NOR flash (w25q256)
  - 2x 15 MB available; but one of the 15 MB regions is the recovery image
* 2T2R 2.4 GHz
  - QCA4019 hw1.0 (SoC)
  - requires special BDF in QCA4019/hw1.0/board-2.bin with
    bus=ahb,bmi-chip-id=0,bmi-board-id=16,variant=PlasmaCloud-PA1200
* 2T2R 5 GHz
  - QCA4019 hw1.0 (SoC)
  - requires special BDF in QCA4019/hw1.0/board-2.bin with
    bus=ahb,bmi-chip-id=0,bmi-board-id=17,variant=PlasmaCloud-PA1200
* 3x GPIO-LEDs for status (cyan, purple, yellow)
* 1x GPIO-button (reset)
* 1x USB (xHCI)
* TTL pins are on board (arrow points to VCC, then follows: GND, TX, RX)
* 2x gigabit ethernet
  - phy@mdio4:
    + Label: Ethernet 1
    + gmac0 (ethaddr) in original firmware
    + used as LAN interface
  - phy@mdio3:
    + Label: Ethernet 2
    + gmac1 (eth1addr) in original firmware
    + 802.3af/at POE(+)
    + used as WAN interface
* 12V/24V 1A DC

Flashing instructions:

The tool ap51-flash (https://github.com/ap51-flash/ap51-flash) should be
used to transfer the factory image to the u-boot when the device boots up.

Signed-off-by: Marek Lindner <marek.lindner@kaiwoo.ai>
[sven@narfation.org: prepare commit message, rebase, use all LEDs, switch
to dualboot_datachk upgrade script, use eth1 as designated WAN interface]
Signed-off-by: Sven Eckelmann <sven@narfation.org>