added optimized saxpy kernel for steamroller

kernel/x86_64/KERNEL.STEAMROLLER

@@ -1,3 +1,4 @@
+SAXPYKERNEL = saxpy.c
 DAXPYKERNEL = daxpy.c
 CAXPYKERNEL = caxpy.c
 ZAXPYKERNEL = zaxpy.c

kernel/x86_64/saxpy.c

@@ -35,7 +35,7 @@ USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 #include "saxpy_microk_haswell-2.c"
 #elif defined(SANDYBRIDGE)
 #include "saxpy_microk_sandy-2.c"
-#elif defined(PILEDRIVER)
+#elif defined(PILEDRIVER) || defined(STEAMROLLER)
 #include "saxpy_microk_piledriver-2.c"
 #endif