ath5k: update dependencies

- Use config symbol defined in the driver instead of arch specific one for
  conditional compilation.
- Rename the ATHEROS_AR231X config symbol to ATH25.
- Fix include (ar231x_platform.h -> ath25_platform.h).
- Some of AR231x SoCs (e.g. AR2315) have PCI bus support, so remove !PCI
  dependency, which block AHB support build.

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/8248/


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