ath79: add support for TP-Link TL-WA701ND/730RE/801ND/901ND v1

ath79: add support for TP-Link TL-WA701ND/730RE/801ND/901ND v1

This adds support for the various clones of the TL-WA830RE recently
supported in fb99ac6807f2 ("ath79: add support for TP-Link TL-WA830RE v1"):

- tplink,tl-wa701nd-v1
- tplink,tl-wa730re-v1
- tplink,tl-wa801nd-v1
- tplink,tl-wa830re-v1 (already supported)
- tplink,tl-wa901nd-v1

Since these devices are 100%-clones in ar71xx, this patch adds all
of them without run-testing (as this has been done for TL-WA830RE v1).

Specifications:
- SOC: Atheros AR7240
- CPU: 400MHz
- Flash: 4 MiB (Spansion S25FL032P)
- RAM: 32 MiB (Zentel A3S56D40FTP-G5)
- WLAN: Atheros AR9280 bgn 2x2
- Ethernet: 1 port (100M)

Flash instructions:
- install from u-boot with tftp (requires serial access)
  > setenv ipaddr a.b.c.d
  > setenv serverip e.f.g.h
  > tftpboot 0x80000000 \
      openwrt-ath79-tiny-tplink_tl-waxxxxx-v1-squashfs-factory.bin
  > erase 0x9f020000 +0x3c0000
  > cp.b 0x80000000 0x9f020000 0x3c0000
  > bootm 0x9f020000
- flash factory image from OEM WebUI
- sysupgrade from ar71xx image

Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>
(backported from commit 2f1cc5c3d5e35d6aa76e794e3d5b4f5856cd38bc)