ath9k: add workaround for AR9331 USB host controller hang with USB1.1 devices

When wifi radio is reset, some bits in (undocumented) USB registers may
flip. Patch adds setting them after radio reset (channel change, up/down).
With this patch stability of USB1.1 full-speed devices, connected directly
to AR9331 host port (no USB2.0 hub) is improved.

See "ar9331's usb stability issue" OpenWrt forum thread for details:
  <https://forum.openwrt.org/viewtopic.php?id=39956>

Based on QCA's Open HAL WAR_USB_DISABLE_PLL_LOCK_DETECT() macro:
  <https://github.com/qca/qcamain_open_hal_public/blob/master/hal/ar9300/ar9300_reset.c#L74>

Adapted to Linux mac80211 driver for 8Devices Carambola2 board by Mantas Pucka:
  <https://github.com/8devices/carambola2/commit/b08b59ceb4e7f0bad4c0b17e703e1e5c4e168923>

Ported to latest OpenWrt BB branch and tested on TP-Link TL-WR703N by
Michel Stempin <michel.stempin@wanadoo.fr>.

Signed-off-by: Michel Stempin <michel.stempin@wanadoo.fr>
[juhosg: refresh and clean up the ath9k patch]
Signed-off-by: Gabor Juhos <juhosg@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@39212 3c298f89-4303-0410-b956-a3cf2f4a3e73
ar71xx: Fix WD My Net N750 weak signal issue

The LNAs need to be enabled by setting their respective GPIO to high even
though the original firmware's setting sets them to low on initialization.

Obviously the LNAs are then later initialized by the driver on the OEM
firmware. Without this fix the device is mostly "deaf".

Signed-off-by: Felix Kaechele <heffer@fedoraproject.org>
Patchwork: http://patchwork.openwrt.org/patch/4688/
Signed-off-by: Gabor Juhos <juhosg@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@39213 3c298f89-4303-0410-b956-a3cf2f4a3e73
ar71xx: Fix WD My Net N600 weak signal issue

The LNAs need to be enabled by setting their respective GPIO to high even
though the original firmware's setting sets them to low on initialization.

Obviously the LNAs are then later initialized by the driver on the OEM
firmware. Without this fix the device is mostly "deaf".

Signed-off-by: Felix Kaechele <heffer@fedoraproject.org>
Tested-by: Steven Haigh <netwiz@crc.id.au>
Patchwork: http://patchwork.openwrt.org/patch/4689/
[juhosg:
  - remove the GPIO LED changes, the My Net N600 has no yellow LEDs at all,
  - change subject and update the commit message]
Signed-off-by: Gabor Juhos <juhosg@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@39214 3c298f89-4303-0410-b956-a3cf2f4a3e73