drm/g94-/disp: calculate some dp audio constants

NVIDIA appear to have tweaked the algorithm from GF110, this implements
the previous algorithm for them still.

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

diff --cc drivers/gpu/drm/nouveau/core/engine/disp/nv50.c
Simple merge

diff --cc drivers/gpu/drm/nouveau/core/engine/disp/nvd0.c
Simple merge