Older radeon boards (r2xx-r5xx) had secondary PCI functions
which we solely there for supporting multi-head on OSs with
special requirements.  Add them to the unsupported list
as well so we don't attempt to bind to them.  The driver
would fail to bind to them anyway, but this does so
in a cleaner way that should not confuse the user.

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