usb: musb: dma: merge ->start/stop into create/destroy

The core code creates a controller and immediately after that it calls
the ->start() callback. This one might drop an error but nobody cares.
The same thing happens in the destroy corner: First ->stop() called
followed by destroy callback. So why not merge those two into the same
function since there is no difference.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Felipe Balbi <balbi@ti.com>