drm/nouveau/msgqueue: support for GP10B PMU firmware

The GP10B firmware is very close to GM20B's. The only difference is that
it supports booting multiple falcons. In order to avoid having too much
functions and structures shared, implement its support in the same
source file as GM20B firmware.

Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>