binconfig.bbclass: Search in installed root instead of S:

binconfig.bbclass: Search in installed root instead of S:
* It is more consistent.
* Fixes subtle binconfig breakages:
  * binconfig were populated with a different name that upstream intended
  * populated binconfig files that were not intended to be populated
  * See http://lists.linuxtogo.org/pipermail/openembedded-devel/2011-April/031972.html

Signed-off-by: Stanislav Brabec <utx@penguin.cz>
Acked-by: Andreas Oberritter <obi@opendreambox.org>
Acked-by: Paul Menzel <paulepanter@users.sourceforge.net>
Acked-by: Enrico Scholz <enrico.scholz@sigma-chemnitz.de>