usb: musb-new: sunxi: Add proper musb exit support

usb: musb-new: sunxi: Add proper musb exit support

musb have platform ops to do proper graceful exit,
so add the exit call and move musb platform exit code
instead of keeping it in driver remove.
This make proper shutdown of musb where .remove will
call disable, exit serially via musb_stop.

Tested-by: Chen-Yu Tsai <wens@csie.org> # A33-OlinuXino
Tested-by: Jagan Teki <jagan@amarulasolutions.com>
Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>