radeon: add missing drm_public exports

Fixes: 9f452648 "radeon: annotate public functions"
Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Cc: Mark Janes <mark.a.janes@intel.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=108006


Signed-off-by: Eric Engestrom <eric.engestrom@intel.com>
Reviewed-by: Michel Dänzer <michel.daenzer@amd.com>
Tested-by: Michel Dänzer <michel.daenzer@amd.com>