ppc/xive2: Fix treatment of PIPR in CPPR update

ppc/xive2: Fix treatment of PIPR in CPPR update

According to the XIVE spec, updating the CPPR should also update the
PIPR. The final value of the PIPR depends on other factors, but it
should never be set to a value that is above the CPPR.

Also added support for redistributing an active group interrupt when it
is precluded as a result of changing the CPPR value.

Signed-off-by: Glenn Miles <milesg@linux.ibm.com>
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
Reviewed-by: Michael Kowal <kowal@linux.ibm.com>
Reviewed-by: Caleb Schlossin <calebs@linux.ibm.com>
Tested-by: Gautam Menghani <gautam@linux.ibm.com>
Link: https://lore.kernel.org/qemu-devel/20250512031100.439842-11-npiggin@gmail.com
Signed-off-by: Cédric Le Goater <clg@redhat.com>