ART: ARM64: Support DotProd SIMD idiom.

Implement support for vectorization idiom which performs dot
product of two vectors and adds the result to wider precision
components in the accumulator.

viz. DOT_PRODUCT([ a1, .. , am], [ x1, .. , xn ], [ y1, .. , yn ]) =
                 [ a1 + sum(xi * yi), .. , am + sum(xj * yj) ],
     for m <= n, non-overlapping sums,
     for either both signed or both unsigned operands x, y.

The patch shows up to 7x performance improvement on a micro
benchmark on Cortex-A57.

Test: 684-checker-simd-dotprod.
Test: test-art-host, test-art-target.

Change-Id: Ibab0d51f537fdecd1d84033197be3ebf5ec4e455
diff --git a/compiler/optimizing/nodes.h b/compiler/optimizing/nodes.h
index 68f1a24..76887f9 100644
--- a/compiler/optimizing/nodes.h
+++ b/compiler/optimizing/nodes.h
@@ -1453,6 +1453,7 @@
   M(VecSetScalars, VecOperation)                                        \
   M(VecMultiplyAccumulate, VecOperation)                                \
   M(VecSADAccumulate, VecOperation)                                     \
+  M(VecDotProd, VecOperation)                                           \
   M(VecLoad, VecMemoryOperation)                                        \
   M(VecStore, VecMemoryOperation)                                       \