LinuxKPI: Add pci_iomap_range function

pci_iomap_range creates a virtual mapping cookie for a PCI BAR.
As compared with pci_iomap it got extra offset parameter.

Sponsored by: Serenity CyberSecurity, LLC
MFC after: 1 week
Reviewed by: manu, bz
Differential Revision: https://reviews.freebsd.org/D45904