pnv/xive2: Print value in invalid register write logging

pnv/xive2: Print value in invalid register write logging

This can make it easier to see what the target system is trying to
do.

[npiggin: split from larger patch]

Signed-off-by: Michael Kowal <kowal@linux.ibm.com>
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
Reviewed-by: Glenn Miles <milesg@linux.ibm.com>
Reviewed-by: Michael Kowal <kowal@linux.ibm.com>
Reviewed-by: Caleb Schlossin <calebs@linux.ibm.com>
Tested-by: Gautam Menghani <gautam@linux.ibm.com>
Link: https://lore.kernel.org/qemu-devel/20250512031100.439842-19-npiggin@gmail.com
Signed-off-by: Cédric Le Goater <clg@redhat.com>