x86, mrst: The shutdown for MRST requires the SCU IPC mechanism

Fix the build failure reported by Randy.

Reported-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Alan Cox <alan@linux.intel.com>
LKML-Reference: <20101115173110.6877.83958.stgit@localhost.localdomain>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>