ppc/xive2: Implement set_os_pending TIMA op

ppc/xive2: Implement set_os_pending TIMA op

xive2 must take into account redistribution of group interrupts if
the VP directed priority exceeds the group interrupt priority after
this operation. The xive1 code is not group aware so implement this
for xive2.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Reviewed-by: Glenn Miles <milesg@linux.ibm.com>
Reviewed-by: Michael Kowal <kowal@linux.ibm.com>
Tested-by: Gautam Menghani <gautam@linux.ibm.com>
Link: https://lore.kernel.org/qemu-devel/20250512031100.439842-47-npiggin@gmail.com
Signed-off-by: Cédric Le Goater <clg@redhat.com>