Add ioctl to conveniently mmap a PCI device BAR into userspace.
Add the ioctl PCIOCBARMMAP on /dev/pci to conveniently create
userspace mapping of a PCI device BAR. This is enormously superior to
read the BAR value with PCIOCREAD and then try to mmap /dev/mem, and
should allow to automatically activate the mapped BARs when needed in
future.
Current implementation creates new sg pager for each user mmap
request. If the pointer (and reference) to a managed device pager is
stored in pci_map, we would be able to revoke all mappings on the BAR
deactivation or relocation. This is related to the unimplemented BAR
activation on mmap, and is postponed for the future.