drm/nouveau/disp: split user classes out from engine implementations

drivers/gpu/drm/nouveau/include/nvkm/engine/disp.h

drivers/gpu/drm/nouveau/nvkm/engine/disp/Kbuild

drivers/gpu/drm/nouveau/nvkm/engine/disp/baseg84.c

drivers/gpu/drm/nouveau/nvkm/engine/disp/basegf119.c

drivers/gpu/drm/nouveau/nvkm/engine/disp/basenv50.c

drivers/gpu/drm/nouveau/nvkm/engine/disp/changf119.c

drivers/gpu/drm/nouveau/nvkm/engine/disp/channv50.c

drivers/gpu/drm/nouveau/nvkm/engine/disp/channv50.h

drivers/gpu/drm/nouveau/nvkm/engine/disp/coreg84.c

drivers/gpu/drm/nouveau/nvkm/engine/disp/coreg94.c

drivers/gpu/drm/nouveau/nvkm/engine/disp/coregf119.c

drivers/gpu/drm/nouveau/nvkm/engine/disp/coregk104.c

drivers/gpu/drm/nouveau/nvkm/engine/disp/corenv50.c

drivers/gpu/drm/nouveau/nvkm/engine/disp/cursgf119.c

drivers/gpu/drm/nouveau/nvkm/engine/disp/cursnv50.c

drivers/gpu/drm/nouveau/nvkm/engine/disp/dmacgf119.c

drivers/gpu/drm/nouveau/nvkm/engine/disp/dmacnv50.c

drivers/gpu/drm/nouveau/nvkm/engine/disp/dmacnv50.h

drivers/gpu/drm/nouveau/nvkm/engine/disp/g84.c

drivers/gpu/drm/nouveau/nvkm/engine/disp/g94.c