drm/radeon/dce3: switch back to old pll allocation order for discrete

The order shouldn't matter, but this seems to cause regressions for
certain specific cases.  This should fix it for now.  We probably
need to investigate a proper fix in the next development cycle.

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: Andy Furniss <andyqos@ukfsn.org>