ath5k: revert AHB bus support removing

This reverts commit 093ec3c5.

AHB bus code has been removed, since we did not have support Atheros
AR231x SoC, required for building the AHB version of ath5k. Now that
support WiSoC chips added we can restore functionality back.

Signed-off-by: Sergey Ryazanov <ryazanov.s.a@gmail.com>
Acked-by: John W. Linville <linville@tuxdriver.com>
Cc: Jiri Slaby <jirislaby@gmail.com>
Cc: Nick Kossifidis <mickflemm@gmail.com>
Cc: "Luis R. Rodriguez" <mcgrof@do-not-panic.com>
Cc: linux-wireless@vger.kernel.org
Cc: ath5k-devel@lists.ath5k.org
Cc: Linux MIPS <linux-mips@linux-mips.org>
Patchwork: https://patchwork.linux-mips.org/patch/8247/


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