pci_cfgreg: Add shims to preserve ABI of pci_cfgreg(read|write)

This is a direct commit to stable/14 to preserve the ABI of the
the pci_cfgregread and pci_cfgregwrite functions. The new routines
are renamed to add a _domain suffix and macros map the new API to
the new functions.

Note: No API compatibility has been provided as modules in ports
should not be using this internal API (normal PCI drivers use
pci_read_config and pci_write_config with a device_t).

(cherry picked from commit b5d2a06b2c4f50fd20774928602a3b5f0f27b127)