LinuxKPI: pci.h split up pcim_iomap_regions_request_all()

Factor out parts of pcim_iomap_regions_request_all() into
pcim_iomap_regions() now needed for a driver.

Sponsored by: The FreeBSD Foundation
MFC after: 7 days
Reviewed by: hselasky
Differential Revision: https://reviews.freebsd.org/D36654