mfd: Add cs5535-mfd driver for AMD Geode's CS5535/CS5536 support

Add an MFD driver to handle the ISA device on CS5535 and CS5536
southbridges. This ISA bridge is actually multiple devices: GPIOs,
MFGPTs, etc.

Signed-off-by: Andres Salomon <dilinger@queued.net>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>