drm/nouveau/nvkm: bump maximum number of NVJPG

RM (and GH100) support 8 NVJPG instances.

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230918202149.4343-4-skeggsb@gmail.com