ar71xx: add support for TP-Link Archer C58 v1

ar71xx: add support for TP-Link Archer C58 v1

TP-Link Archer C58 v1 is a dual-band AC1350 router, based on Qualcomm
QCA9561 + QCA9886. It looks like Archer C59 v1 without USB port.

Specification:

- 775/650/258 MHz (CPU/DDR/AHB)
- 64 MB of RAM (DDR2)
- 8 MB of FLASH (SPI NOR)
- 3T3R 2.4 GHz
- 2T2R 5 GHz
- 5x 10/100 Mbps Ethernet
- 6x LED, 3x button
- UART header on PCB, RX, TX at TP4+5 (backside)

QCA9886 wlan needs pre_cal_data file and enable ieee80211 phy hotplug to
patch macaddress.

Flash instruction:

Use "factory" image directly in vendor GUI.

Recovery method:

1. Set PC to fixed ip address 192.168.0.66/24.
2. Download "lede-ar71xx-generic-archer-c58-v1-squashfs-factory.bin" and
   rename it to "tp_recovery.bin".
3. Start a tftp server with the file "tp_recovery.bin" in its root
   directory.
4. Turn off the router.
5. Press and hold Reset button.
6. Turn on router with the reset button pressed and wait ~15 seconds.
7. Release the reset button and after a short time the firmware should
   be transferred from the tftp server.
8. Wait ~30 second to complete recovery.

Flash instruction under U-Boot, using UART:

tftp 0x81000000 lede-ar71xx-...-sysupgrade.bin
erase 0x9f020000 +$filesize
cp.b $fileaddr 0x9f020000 $filesize
reset

This commit is based on GitHub PR#1112

Signed-off-by: Henryk Heisig <hyniu@o2.pl>