greybus: improve module cleanup code

greybus: improve module cleanup code

When a module gets destroyed all of its state and the state of its
interfaces and connections (etc.) need to be torn down.  This is
not now being done properly.  Add this teardown code.

Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: Greg Kroah-Hartman <greg@kroah.com>