hw/cxl: Make the CXL fixed memory window setup a machine parameter.

Paolo Bonzini requested this change to simplify the ongoing
effort to allow machine setup entirely via RPC.

Includes shortening the command line form cxl-fixed-memory-window
to cxl-fmw as the command lines are extremely long even with this
change.

The json change is needed to ensure that there is
a CXLFixedMemoryWindowOptionsList even though the actual
element in the json is never used. Similar to existing
SgxEpcProperties.

Update qemu-options.hx to reflect that this is now a -machine
parameter.  The bulk of -M / -machine parameters are documented
under machine, so use that in preference to M.

Update cxl-test and bios-tables-test to reflect new parameters.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Ben Widawsky <ben@bwidawsk.net>
Reviewed-by: Davidlohr Bueso <dave@stgolabs.net>
Message-Id: <20220608145440.26106-2-Jonathan.Cameron@huawei.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>