ACPI, PCI, x86: move MCFG parsing routine from ACPI to PCI file

Move
arch/x86/kernel/acpi/boot.c: acpi_parse_mcfg()
to
arch/x86/pci/mmconfig-shared.c: pci_parse_mcfg()
where it is used, and make it static.

Move associated globals and helper routine with it.

No functional change.

This code move is in preparation for SFI support,
which will allow the PCI code to find the MCFG table
on systems which do not support ACPI.

Signed-off-by: Len Brown <len.brown@intel.com>
Acked-by: Jesse Barnes <jbarnes@virtuousgeek.org>