pnv/xive: Support cache flush and queue sync inject with notifications

pnv/xive: Support cache flush and queue sync inject with notifications

Adds support for writing a completion notification byte in memory
whenever a cache flush or queue sync inject operation is requested by
software.  QEMU does not cache any of the XIVE data that is in memory and
therefore it simply writes the completion notification byte at the time
that the operation is requested.

Co-authored-by: Glenn Miles <milesg@linux.vnet.ibm.com>
Signed-off-by: Glenn Miles <milesg@linux.vnet.ibm.com>
Signed-off-by: Michael Kowal <kowal@linux.vnet.ibm.com>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>