LU-1199 rpm: don't open-code %_smp_mflags

LU-1199 rpm: don't open-code %_smp_mflags

In some distant past, %_smp_mflags didn't exist on all
supported platforms.

We can use it now. The only difference is the lack of an
8-CPU limit, which can be overridden by explicitly defining
RPM_BUILD_NCPUS anyway.

Signed-off-by: Jeff Mahoney <jeffm@suse.com>
Signed-off-by: James Simmons <uja.ornl@gmail.com>
Change-Id: I0b5c2f879da9ba6e8aa3103bfe59e6b43f8d72bc
Reviewed-on: http://review.whamcloud.com/5492
Tested-by: Jenkins
Reviewed-by: Christopher J. Morrone <chris.morrone.llnl@gmail.com>
Reviewed-by: Bob Glossman <bob.glossman@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>