sed: changes to support merged /usr

sed: changes to support merged /usr

Few of the perl scripts referring '#!/bin/sed' inside the script. But when
'usrmerge' feature is enabled this path would be /usr/bin/sed. So to satisfy
build dependency add '/bin/sed' to it's providers list.

Signed-off-by: Amarnath Valluri <amarnath.valluri@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>