drm: Remove the macro defintion of DRM_DEBUG_MODE

Two macro definitions of DRM_DEBUG_KMS/MODE can be used to add the debug
info related with KMS. It is confusing.
So remove the macro definition of DRM_DEBUG_MODE. Instead it can be replaced
by the DRM_DEBUG_KMS.

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>