ipq40xx: add support for Linksys EA6350v3

ipq40xx: add support for Linksys EA6350v3

Specifications:
SOC: Qualcomm IPQ4018
RAM: 256 MiB Samsung K4B2G1646F-BYK0
FLASH1: MX25L1605D 2 MB
FLASH2: Winbond W25N01GV 128Mb
ETH: Qualcomm QCA8075
WLAN0: Qualcomm Atheros QCA4018 2.4GHz 802.11b/g/n 2x2
WLAN1: Qualcomm Atheros QCA4018 5GHz 802.11n/ac W2 2x2
INPUT: WPS, Reset
LED: Status - Green
SERIAL: Header at J19, Beneath DC Power Jack
        1-VCC ; 2-TX ; 3-RX; 4-GND;
        Serial 115200-8-N-1.

Tested and working:
- USB (requires extra packages)
- LAN Ethernet (Correct MAC-address)
- WAN Ethernet (Correct MAC-address)
- 2.4 GHz WiFi (Correct MAC-address)
- 5 GHz WiFi (Correct MAC-address)
- Factory installation from Web UI
- OpenWRT sysupgrade
- LED
- Reset Button

Need Testing:
- WPS button

Install via Web UI:
- Attach to a LAN port on the router.
- Connect to the Linksys Smart WiFi Page (default 192.168.1.1) and login
- Select the connectivity tab on the left
- In the manual update box on the right
- Select browse, and browse to
  openwrt-ipq40xx-linksys_ea6350v3-squashfs-factory.bin
- Click update.
- Read and accept the warning
- The router LED will start blinking. When the router LED goes solid, you
  can now navigate to 192.168.1.1 to your new OpenWrt installation.

Sysupgrade:
- Flash the sysupgrade image as usual. Please: try to do a reset everytime
  you can (doing it with LuCI is easy and can be done in the same step).

Recovery (Automatic):
- If the device fails to boot after install or upgrade, whilst the unit is
  turned on:
1 - Wait 15 seconds
2 - Switch Off and Wait 10 seconds
3 - Switch on
4 - Repeat steps 1 to 3, 3 times then go to 5.
5 - U-boot will have now erased the failed update and switched back to the
    last working firmware - you should be able to access your router on
    LAN.

Recovery (Manual):
- The steps for manual recovery are the same as the generic u-boot tftp
  client method.

Back To Stock:
- Use the generic recovery using the tftp client method to flash the
  "civic.img". Also you can strip-and-pad the original image and use
  the generic "mtd" method by flashing over the "kernel" partition.
* Just be careful to flash in the partition that the device is currently
  booted.

Signed-off-by: Ryan Pannell <ryan@osukl.com>
Signed-off-by: Oever González <notengobattery@gmail.com>
[minor edits, removed second compatible of nand, added dtb entry to 4.19]
Signed-off-by: Christian Lamparter <chunkeey@gmail.com>