ppc/xive: Check TIMA operations validity

ppc/xive: Check TIMA operations validity

Certain TIMA operations should only be performed when a ring is valid,
others when the ring is invalid, and they are considered undefined if
used incorrectly. Add checks for this condition.

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/20250512031100.439842-44-npiggin@gmail.com
Signed-off-by: Cédric Le Goater <clg@redhat.com>