drm/radeon/kms: add primary dac adj values table

Look up primary dac adj values from the table if
there is no bios or bios dac table to reference.

The lookup table may need to be adjusted for certain
families.

Should fix kernel bug 14945.

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