Clean up the pci host generic driver

• Support Prefetchable Memory.
• Use the correct rman when allocating memory and ioports.
• Translate PCI addresses in bus_alloc_resource to allow physical addresses that are different than pci addresses.

Reviewed by: Robert Crowston <crowston_protonmail.com>
Sponsored by: Innovate UK
Differential Revision: https://reviews.freebsd.org/D25121