ppc/xive2: redistribute group interrupts on context push

ppc/xive2: redistribute group interrupts on context push

When pushing a context, any presented group interrupt should be
redistributed before processing pending interrupts to present
highest priority.

This can occur when pushing the POOL ring when the valid PHYS
ring has a group interrupt presented, because they share signal
registers.

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/20250512031100.439842-46-npiggin@gmail.com
Signed-off-by: Cédric Le Goater <clg@redhat.com>