hw/fsi: Introduce IBM's FSI Bus

hw/fsi: Introduce IBM's FSI Bus

This is a part of patchset where FSI bus is introduced.

The FSI bus is a simple bus where FSI master is attached.

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: - removed include/hw/fsi/engine-scratchpad.h and
       	 hw/fsi/engine-scratchpad.c
       - dropped FSI_SCRATCHPAD
       - included FSIBus definition
       - dropped hw/fsi/trace-events changes ]
Signed-off-by: Cédric Le Goater <clg@kaod.org>