i386/pc: Enable CXL fixed memory windows

Add the CFMWs memory regions to the memorymap and adjust the
PCI window to avoid hitting the same memory.

Signed-off-by: Jonathan Cameron <jonathan.cameron@huawei.com>
Message-Id: <20220429144110.25167-36-Jonathan.Cameron@huawei.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>