x86/mrst/pci: avoid SoC fixups on non-SoC platforms

The PCI fixups get executed based upon whether they are linked in. We need
to avoid executing them if we boot a dual SoC/PC type kernel on a PC class
system.

Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>