drm/radeon: don't share plls if monitors differ in audio support

Enabling audio may enable different pll dividers.  Don't share
plls if the monitors differ in audio support.

bug:
https://bugzilla.kernel.org/show_bug.cgi?id=98751



Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org