drm: Remove the unused prefix in DRM_DEBUG_KMS/DRIVER/MODE

We will have to add a prefix when using the macro defintion of DRM_DEBUG_KMS
/DRM_DEBUG_DRIVER/MODE. It is not convenient. We should use the DRM_NAME
as default prefix.
So remove the prefix in the macro definition of DRM_DEBUG_KMS/DRIVER/MODE.

Signed-off-by: Zhao Yakui <yakui.zhao@intel.com>
Acked-by: Ian Romanick <ian.d.romanick@intel.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>