Change way extra symbols are included in build.  Use
KBUILD_EXTRA_SYMBOLS to directly included Modules.symvers
files instead of buildling Modules.symvers in buildroot
directory.

Signed-off-by: Nathaniel Clark <nathaniel.l.clark@intel.com>
Change-Id: I4a6ee59f4e4eed9f878ad52993b8b17426f19d4a
Reviewed-on: http://review.whamcloud.com/15498


Tested-by: Jenkins
Reviewed-by: Dmitry Eremin <dmitry.eremin@intel.com>
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>