drm/radeon: properly validate the atpx interface

Some bioses don't set the function mask correctly
which caused required functions to be disabled.

Fixes:
https://bugzilla.kernel.org/show_bug.cgi?id=53111

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