drm/nouveau/fifo/tu102-: prepare for GSP-RM

- (temporarily) disable if GSP-RM detected, will be added later
- add dtor() so GSP-RM paths can cleanup properly
- add alternate engine context mapping interface for RM engines
- add alternate chid interfaces to handle RM USERD oddities

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230918202149.4343-26-skeggsb@gmail.com