ACPI / LPSS: Make PCI dependency explicit

After commit 5d32a665 (PCI/ACPI: Allow ACPI to be built without
CONFIG_PCI set), it is possible to build ACPI without any PCI support.

This code depends on PCI. Compile only when PCI is present.

Fixes: 5d32a665 ("PCI/ACPI: Allow ACPI to be built without CONFIG_PCI set")
Signed-off-by: Sinan Kaya <okaya@kernel.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>