hw/fsi: Introduce IBM's Local bus

hw/fsi: Introduce IBM's Local bus

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

The LBUS is modelled to maintain mapped memory for the devices. The
memory is mapped after CFAM config, peek table and FSI slave registers.

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 lbus_add_device() bc unused
       - removed lbus_create_device() bc used only once
       - removed "address" property
       - updated meson.build to build fsi dir
       - included an empty hw/fsi/trace-events ]
Signed-off-by: Cédric Le Goater <clg@kaod.org>