greybus: svc: Read and clear module's boot status

As per the module's boot sequence diagram, the AP needs to read/clear
T_TstSrcIncrement attribute on hotplug (svc) events.

Implement that.

FIXME: This is module-hardware dependent and needs to be extended for
every type of module we want to support.

[ Based on work by Marti & Eli to clear the attribute with DME set]
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Reviewed-by: Johan Hovold <johan@hovoldconsulting.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>