x86, pci: Exclude Moorestown PCI code if CONFIG_X86_MRST=n

If we don't have any Moorestown CPU support compiled in, we don't need
the Moorestown PCI support either.

Signed-off-by: Yinghai Lu <yinghai@kernel.org>
LKML-Reference: <4B858E89.7040807@kernel.org>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>