greybus: es1: separate stopping and deallocating urbs

Separate stopping and deallocating our in-urbs.

This will facilitate implementing proper host-device life-time management.

Compile-only tested.

Signed-off-by: Johan Hovold <johan@hovoldconsulting.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>