Benchtests: Increase benchmark iterations

Increase benchmark iterations for math and vector math functions to improve
timing accuracy.  Vector math benchmarks now take 1-3 seconds on a modern CPU.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

benchtests/bench-libmvec-skeleton.c

@@ -29,7 +29,7 @@
 #include <bench-libmvec-arch.h>
 
 #include <bench-util.c>
-#define D_ITERS 10000
+#define D_ITERS 200000
 
 int
 main (int argc, char **argv)

benchtests/bench-skeleton.c

@@ -48,7 +48,7 @@ main (int argc, char **argv)
 
   memset (&runtime, 0, sizeof (runtime));
 
-  unsigned long iters = 1000;
+  unsigned long iters = 2000;
 
 #ifdef BENCH_INIT
   BENCH_INIT ();