drm/amdgpu: further ring test cleanups

Move all error messages from IP specific code into the common helper.
This way we now uses the ring name in the messages instead of the index
and note which device is affected as well.

Also cleanup error handling in the IP specific code and consequently use
ETIMEDOUT when the ring test timed out.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Andrey Grodzovsky <andrey.grodzovsky@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>