x86/pci: Reorder pci_mmcfg_arch_map() definition before calls

The typical style is to define functions before calling them.  Move
pci_mmcfg_arch_map() and pci_mmcfg_arch_unmap() earlier so they're defined
before they're called.  No functional change intended.

Link: https://lore.kernel.org/r/20231121183643.249006-10-helgaas@kernel.org


Tested-by: Tomasz Pala <gotar@polanet.pl>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>