MIPS: ath79: register platform devices for the PCI controllers

The pci-ar71xx and pci-ar724x drivers were converted
into platform drivers. Register the corresponding
platform devices for the PCI controllers instead
of using the ar7{1x,24}x_pcibios_init functions.

Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
Patchwork: http://patchwork.linux-mips.org/patch/4908/
Signed-off-by: John Crispin <blogic@openwrt.org>