ipq807x: add support for TP-Link EAP620 HD v1

ipq807x: add support for TP-Link EAP620 HD v1
Specifications:
  * SoC: Qualcomm IPQ8072A (64-bit Quad-core Arm Cortex-A53 @ 1.4 GHz)
  * Memory: 2x ESMT M15T4G16256A-DEBG2G (1 GiB DDR3-1866 13-13-13)
  * Serial Port: 3v3 TTL 115200n8
  * Wi-Fi: QCA5054 (4x4 5 GHz 802.11ax)
  * Wi-Fi: QCN5024 (2x2 2.4 GHz 802.11b/g/n/ax)
  * Ethernet: AR8031 (10/100/1000BASE-T)
  * Flash: Winbond W29N01HZSINF (128 MiB)
  * LEDs: 1x Blue Status (GPIO 42 Active High)
  * Buttons: 1x Reset (GPIO 50 Active Low)

Installation Instructions (Serial+TFTP):
  1. Solder 4 pin header to JP1 and bridge pads of R58 and R62.
  2. Connect 3V3 TTL port to TX, RX, and GND, which are positions 1, 2, and 3 respectively.
     Be sure to crossover TX and RX.
  3. Copy RAM firmware
     openwrt-qualcommax-ipq807x-tplink_eap620hd-v1-initramfs-uImage.itb
     to a TFTP server's root that is in the same subnet as your AP.
  4. Power up the AP hold Ctrl+B in the serial console (115200n8) until autoboot is halted.
  5. Run the following commands in the U-boot prompt:
     # setenv serverip <TFTP server addr>
     # setenv ipaddr <addr of AP>
     # tftpboot 0x44000000 openwrt-qualcommax-ipq807x-tplink_eap620hd-v1-initramfs-uImage.itb
     # bootm
     You may need to type Ctrl+C and Enter before running these commands
     to clear invisible characters from the buffer.
  6. Run the following command in a terminal to copy the sysupgrade image
     to be installed (check IP address):
     $ scp -O openwrt-qualcommax-ipq807x-tplink_eap620hd-v1-squashfs-sysupgrade.bin root@192.168.1.1:/tmp/
  7. Activate the OpenWrt serial console and run the following commands:
     # cd /tmp
     # sysupgrade -n openwrt-qualcommax-ipq807x-tplink_eap620hd-v1-squashfs-sysupgrade.bin
  8. The AP will reboot and OpenWrt will be successfully installed.

Known Issues:
  * 5GHz radio instability (upstream current ath11k build bug maybe?)

Device support directly followed from EAP660HDv1 support
Links: #15832

Signed-off-by: Shymon Samsel <ssamsel@umass.edu>
Link: https://github.com/openwrt/openwrt/pull/17254
Signed-off-by: Robert Marko <robimarko@gmail.com>