ath79: add support for Netgear R6100

ath79: add support for Netgear R6100

Netgear R6100 is a dual-band Wi-Fi 5 (AC1200) router based on Qualcomm
Atheros (AR9344 + QCA9882) platform. Support for this device was first
introduced in 15f6f67d18 (ar71xx). FCC ID: PY312400225.

Specifications:

- Atheros AR9344 (560 MHz)
- 128 MB of RAM (DDR2)
- 128 MB of flash (parallel NAND)
- 2T2R 2.4 GHz Wi-Fi (AR9344)
- 2T2R 5 GHz Wi-Fi (QCA9882)
- 5x 10/100 Mbps Ethernet (AR9344)
- 4x internal antenna
- 1x USB 2.0 (GPIO-controlled power)
- 6x LED, 3x button (reset, Wi-Fi, WPS)
- UART (4-pin, 2.54 mm pitch) header on PCB
- 1x mechanical power switch
- DC jack for main power input (12 V)

WARNING: sysupgrade from older stable releases is not possible, fresh
installation (via vendor's GUI or TFTP based recovery) is required.
Reason for that is increased kernel partition size.

Installation:

Use the 'factory' image under vendor's GUI or via TFTP U-Boot recovery.
You can use the 'nmrpflash' tool at a boot time, before kernel is loaded
or start it manually by pressing the 'reset' button for ~20 seconds from
powering up the device (U-Boot will start TFTP server on 192.168.1.1,
use TFTP client to send the image).

Signed-off-by: Enrico Mioso <mrkiko.rs@gmail.com>
Signed-off-by: Zoltan HERPAI <wigyori@uid0.hu>
Signed-off-by: Michael Pratt <mcpratt@pm.me>
Signed-off-by: Piotr Dymacz <pepe2k@gmail.com>