drm/radeon/kms/atom: loosen pll min output limits

drm/radeon/kms/atom: loosen pll min output limits

Limiting the pll output range is a good thing generally as
it limits the number of possible pll combinations for a given
frequency presumably to the ones that work best on each card.
That's why the limits are in the bios tables. However, certain
duallink DVI monitors seem to like pll combinations that would
be limited by this at least on pre-DCE 3.0 r6xx hardware.  This
might need to be adjusted per family or per clock range in the
future.

See fdo bug 24727.

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