uboot-imx

Add a comment for board_quiesce_devices()

This exported function should have a comment describing what it does. Also
it should really be removed in favour of device_remove(), which handles
this sort of thing now. Add a comment with a TODO.

Signed-off-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Alexander Graf <agraf@suse.de>