Add support for XHCI that exists on a PCI bus
Ask PCI manager if there are any XHCI controllers to attach to, then continue to HAL described ones once they're all done. Similarly ask around for the PCI root hub name. xhci.c: Root hub name now in a RAM variable. Workaround for DMA controller problem with VL805 if the array of structure pointers is only 8 byte aligned. xhcimodule.c/h: Do 2 pass discovery, PCI first, then HAL descriptors. Speed up interrupt despatch a bit by calling the HAL's enable/disable directly rather than via _swix(OS_Hardware). Explicitly clear the interrupt too for the case where it's latched in the PCI peripheral.