ppc/xive2: Enable lower level contexts on VP push

ppc/xive2: Enable lower level contexts on VP push

When pushing a context, the lower-level context becomes valid if it
had V=1, and so on. Iterate lower level contexts and send them
pending interrupts if they become enabled.

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/20250512031100.439842-51-npiggin@gmail.com
Signed-off-by: Cédric Le Goater <clg@redhat.com>