greybus: Documentation: move the interface power attributes

Move the interface power attributes after the other interface attributes
to keep the attributes grouped by device type.

Signed-off-by: Johan Hovold <johan@hovoldconsulting.com>
Reviewed-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>