drm/radeon: move radeon_ib_ring_tests out of chipset code

Making it easier to control when it is executed.

Signed-off-by: Christian König <deathsimple@vodafone.de>
Reviewed-by: Michel Dänzer <michel.daenzer@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>