The core/mem/shader clocks don't support the fractional feedback divider,
causing our calculated clocks to be off by quite a lot in some cases. To
solve this we will switch to a search-based algorithm when fN is NULL.
For my NVA8 at PL3, this actually generates identical cooefficients to
the binary driver. Hopefully that's a good sign, and that does not
break VPLL calculation for someone..
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
