set GEMM_PREFERED_SIZE for HASWELL

Haswell likes a GEMM_PREFERED_SIZE of 16 to improve the split that the
threading code does to make it a nice multiple of the SIMD kernel size

param.h

@@ -1508,6 +1508,7 @@ USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 #define SYMV_P  8
 
 #define SWITCH_RATIO	32
+#define GEMM_PREFERED_SIZE	16
 
 #ifdef ARCH_X86