Move pci_map_physmem(), pci_unmap_physmem(), and
sandbox_set_enable_pci_map() from u-boot-sandbox.h to a new file
sandbox_pci.h to simplify dependencies.
Fix the header order in the PCI emul file while we are here.
Co-developed-by: Claude <noreply@anthropic.com>
Signed-off-by: Simon Glass <sjg@chromium.org>