drm/radeon/kms: add new pll algo for avivo asics

Based on the vbios code.  This should hopefully
fix the pll problems on a number of avivo asics
once it's enabled.

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