pci_mmio_cfg: Move guard around pci_s_* functions to x86

There is no platform in our tree that requires the PCI MMIO ops but
doesn't want the pci_s_* definitions. The only case where we include
the `pci_mmio_cfg.h` header but don't want the pci_s_* functions to
use MMIO is on older x86 platforms, so move the guard there.

Change-Id: Iaeed6ab43ad61b7c0e14572b12bf4ec06b6a26af
Signed-off-by: Nico Huber <nico.huber@secunet.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/58331
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Shelley Chen <shchen@google.com>
Reviewed-by: Tim Wawrzynczak <twawrzynczak@chromium.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>

src/arch/x86/include/arch/pci_ops.h

@@ -4,6 +4,8 @@
 #define ARCH_I386_PCI_OPS_H
 
 #include <arch/pci_io_cfg.h>
+#if CONFIG(MMCONF_SUPPORT)
 #include <device/pci_mmio_cfg.h>
+#endif
 
 #endif /* ARCH_I386_PCI_OPS_H */