hw/cxl/events: Add event interrupt support

hw/cxl/events: Add event interrupt support

Replace the stubbed out CXL Get/Set Event interrupt policy mailbox
commands.  Enable those commands to control interrupts for each of the
event log types.

Skip the standard input mailbox length on the Set command due to DCD
being optional.  Perform the checks separately.

Signed-off-by: Ira Weiny <ira.weiny@intel.com>
Reviewed-by: Fan Ni <fan.ni@samsung.com>
Reviewed-by: Davidlohr Bueso <dave@stgolabs.net>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Message-Id: <20230530133603.16934-5-Jonathan.Cameron@huawei.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>