MIPS: ath79: rename pci-ath724x.h

The declared function in this header file is used by the
ath79 platform code only. Move the header to the platform
directory.

Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
Acked-by: René Bolldorf <xsecute@googlemail.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/3486/


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