LU-3953 build: look for kconfig.h in $LINUX

LU-3953 build: look for kconfig.h in $LINUX

On SLES systems, the kernel source and objects are not in the same
directory. kconfig.h is in the source tree, not the object tree.

Signed-off-by: Jeff Mahoney <jeffm@suse.com>
Signed-off-by: James Simmons <uja.ornl@gmail.com>
Change-Id: I9c382a319181ff2d9958821a40d4eef6877f5867
Reviewed-on: http://review.whamcloud.com/10159
Reviewed-by: Bob Glossman <bob.glossman@intel.com>
Tested-by: Jenkins
Reviewed-by: Dmitry Eremin <dmitry.eremin@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Yang Sheng <yang.sheng@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>