ath79: add support for Archer C58/C59 v1

ath79: add support for Archer C58/C59 v1

This commit adds support for the Archer C58 v1 and C59 v1, previously
supported in the ar71xx target.

CPU:   Qualcomm QCA9561
RAM:   64M (C58) / 128M (C59)
FLASH: 8M (C58) / 16M (C59)
WiFi:  QCA9561 bgn 3x3:3
       QCA9888 nac 2x2:2
LED:   Power, WiFi 2.4, WiFi 5, WAN green, WAN amber, LAN, WPS
       Only C59: USB
BTN:   WPS, WiFi, Reset

Installation
------------

Via Web-UI:
Update factory image via Web-UI.

Via TFTP:
Rename factory image to "tp_recovery.bin" and place it in the root-dir
of your tftp server. Configure to listen on 192.168.0.66. Power up the
router while holding down the reset-button. The router will flash itself
and reboot.

Note: For TFTP, you might need a switch between router and computer, as
link establishment might take to long.

Signed-off-by: David Bauer <mail@david-bauer.net>