[U-Boot] "Un-initialization" of hardware block prior to launching linux

[Steve Sakoman]

Beagle currently enables musb gadget support in u-boot in order to
support console communication over USB.

The musb hardware remains in an active state as linux is launched.
I've had complaints from those working on Linux power management -- it
seems that leaving things active prevents the kernel from entering
full chip retention.

Is there an approved mechanism for shutting down hardware gracefully
prior to launching linux?

The console gadget seems somewhat of a special case since you really
want it to remain active till the very last moment so error messages
can be displayed.

Steve