ppc/xive2: Prevent pulling of pool context losing phys interrupt

ppc/xive2: Prevent pulling of pool context losing phys interrupt

When the pool context is pulled, the shared pool/phys signal is
reset, which loses the qemu irq if a phys interrupt was presented.

Only reset the signal if a poll irq was presented.

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/20250512031100.439842-42-npiggin@gmail.com
Signed-off-by: Cédric Le Goater <clg@redhat.com>