ar71xx: add AR724x PCIe init fixes

Add upstream send AR724x PCIe patches to get the PCIe controller out of
reset during driver init.

The AVM Fritz 300E bootloader doesn't take care of releasing the
different PCIe controller related resets which causes an endless hang
as soon as either the PCIE Reset register (0x180f0018) or the PCI
Application Control register (0x180f0000) is read from.

Signed-off-by: Mathias Kresin <dev@kresin.me>