dmaengine: pl330: Delete unused functions

The functions _queue_empty(), _emit_ADDH(), _emit_NOP(), _emit_STZ()
and _emit_WFE() are not used. Delete them.

Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>