x86/config: Select MSIC MFD driver on Intel Medfield platform

On Intel Medfield platform we use MSIC MFD driver to create
necessary platform devices so it is essential to have the driver
compiled into the kernel.

Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Alan Cox <alan@linux.intel.com>
Cc: jacob.jun.pan@linux.intel.com
Link: http://lkml.kernel.org/n/tip-7hp1otk4wf4mg5pqohcwt06w@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@elte.hu>