dmaengine: pl330: Remove pl330_chan_ctrl()

The pl330_chan_ctrl() function has 3 internal code paths which, except for the
locking, do not share any code outside of their sections. One code path is never
exercised and can be removed. The other two are mostly just forwards to the
_start() and _stop() calls. This patch modifies the code to instead of going via
pl330_chan_ctrl() to call _start() and _stop() directly. This allows to
completely remove pl330_chan_ctrl().

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>