kernel: mac80211: backport ath9k device tree support patches

kernel: mac80211: backport ath9k device tree support patches

These patches add support for configuring ath9k based devices via
devicetree. This was tested on PCI(e) based devices. This should work
for AHB based devices as well (adding more AHB specific properties may
still be needed) as soon as the ath79 platform is ready to populate the
ath9k wmac via devicetree.
This patchset was accepted upstream, more information can be found on
the linux-wireless list:
https://www.spinics.net/lists/linux-wireless/msg155474.html

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>