drm/nouveau/core: recognise TU116 chipset

Modesetting only, still waiting on ACR/GR firmware from NVIDIA for Turing
graphics/compute bring-up.

Each subsystem was compared with traces, along with various tests to check
that things generally work as they should, and appears compatible enough
with the current TU117 code to enable support.

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>