drm/nouveau/core: add SEC2 engine

SEC2 is the name given by NVIDIA to the SEC engine post-Fermi (reasons
unknown). Even though it shares the same address range as SEC, its usage
is quite different and this justifies a new engine. Add this engine and
make TOP use it all post-TOP devices should use this implementation and
not the older SEC.

Also quickly add the short gp102 implementation which will be used for
falcon booting purposes.

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