drm/radeon/atombios: declare connector convert tables as static

The tables:
 * supported_devices_connector_convert
 * supported_devices_connector_object_id_convert
 * object_connector_convert
are used in redeon_atombios.c only, so declare them as static.

Signed-off-by: Michele Curti <michele.curti@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>