drm/nouveau/gsp: add common code for engines/engine objects

With minimal to no direct HW programming required, most nvkm_engine
implementations are nearly identical when running on top of GSP-RM.

Add a common implementation of the boilerplate, and use nvkm_rm_gpu to
expose the correct class IDs.

As they're now handled by common code, and there's no support for them
prior to GSP-RM support - this deletes the GA100 NVDEC/NVJPG/OFA HALs,
the GA102 NVENC/OFA HALs, and the AD102 GR/NVDEC/NVENC/NVJPG/OFA HALs.

Signed-off-by: Ben Skeggs <bskeggs@nvidia.com>
Reviewed-by: Dave Airlie <airlied@redhat.com>
Reviewed-by: Timur Tabi <ttabi@nvidia.com>
Tested-by: Timur Tabi <ttabi@nvidia.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>