Fred and Nick have been hacking baremetal POWER systems (OPAL) for
many years. They use and modify the QEMU models regularly. Add them as
PowerNV reviewers.

Cc: Frédéric Barrat <fbarrat@linux.ibm.com>
Cc: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Cédric Le Goater <clg@kaod.org>
Acked-by: Frederic Barrat <fbarrat@linux.ibm.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Cédric Le Goater <clg@kaod.org>