A lot of mfd drivers select MFD_CORE which however depends on
GENERIC_HARDIRQS support.
So add the missing dependency to all drivers to get rid of
this link error:

ERROR: "irq_create_mapping" [drivers/mfd/mfd-core.ko] undefined!
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>