[ARM] 5127/1: Core MFD support

This patch provides a common subdevice registration system for MFD type
chips, using platfrom device.

Signed-off-by: Ian Molton <spyro@f2s.com>
Signed-off-by: Dmitry Baryshkov <dbaryshkov@gmail.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>