MIPS: ath79: Add AR933x specific WMAC setup code

The wireless MAC of the AR933x SoCs uses different base address, and
requires different setup code.

Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
Cc: Imre Kaloz <kaloz@openwrt.org>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/3030/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>