hw/fsi: Introduce IBM's scratchpad device

hw/fsi: Introduce IBM's scratchpad device

This is a part of patchset where IBM's Flexible Service Interface is
introduced.

The scratchpad provides a set of non-functional registers. The firmware
is free to use them, hardware does not support any special management
support. The scratchpad registers can be read or written from LBUS
slave. The scratch pad is managed under FSI CFAM state.

Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
Signed-off-by: Ninad Palsule <ninad@linux.ibm.com>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
[ clg: - moved object FSIScratchPad under FSICFAMState
       - moved FSIScratchPad code under cfam.c ]
Signed-off-by: Cédric Le Goater <clg@kaod.org>