mips: dts: qca: add wmac support

Now that OF ahb support was added to the ath9k driver, we can use it to
enable and use the SoC wireless found in these chipsets.

Signed-off-by: Rosen Penev <rosenp@gmail.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>