x86, mrst: Fix dependencies of "select INTEL_SCU_IPC"

x86, mrst: Fix dependencies of "select INTEL_SCU_IPC"

commit b9fc71f47 (x86, mrst: The shutdown for MRST requires the SCU
IPC mechanism) introduced the following warning:

 warning: (X86_MRST && PCI && PCI_GOANY && X86_32 &&
 X86_EXTENDED_PLATFORM && X86_IO_APIC) selects INTEL_SCU_IPC which has
 unmet direct dependencies (X86 && X86_PLATFORM_DEVICES && X86_MRST)

which is due to the hierarchical menu structure.

Select X86_PLATFORM_DEVICES as well.

Originally-from: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
LKML-Reference: <20101115101406.77e072ef.randy.dunlap@oracle.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>