drm/radeon/kms: remove new pll algo

The recent changes to the old algo (prefer high post div)
coupled with the range and precision limitations of using
fixed point with the new algo make the new algo less
useful.  So drop the new algo.  This should work as well
or better than the old new/old combinations and simplifies
the code a lot.

Fixes:
https://bugs.freedesktop.org/show_bug.cgi?id=30218
among others.

Signed-off-by: Alex Deucher <alexdeucher@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>