MIPS: pci-ar724x: use dynamically allocated PCI controller structure

The current code uses static variables to store the
PCI controller specific data. This works if the system
contains one PCI controller only, however it becomes
impractical when multiple PCI controllers are present.

Move the variables into a dynamically allocated controller
specific structure, and use that instead of the static
variables.

Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
Patchwork: http://patchwork.linux-mips.org/patch/4912/
Signed-off-by: John Crispin <blogic@openwrt.org>