Basic SIMD reduction support.

Rationale:
Enables vectorization of x += .... for very basic (simple, same-type)
constructs. Paves the way for more complex (narrower and/or mixed-type)
constructs, which will be handled by the next CL.

This is  a revert   of Icb5d6c805516db0a1d911c3ede9a246ccef89a22
and thus a revert^2 of I2454778dd0ef1da915c178c7274e1cf33e271d0f
and thus a revert^3 of I1c1c87b6323e01442e8fbd94869ddc9e760ea1fc
and thus a revert^4 of I7880c135aee3ed0a39da9ae5b468cbf80e613766

PS1-2 shows what needed to change

Test: test-art-host test-art-target

Bug: 64091002
Change-Id: I647889e0da0959ca405b70081b79c7d3c9bcb2e9
diff --git a/compiler/optimizing/scheduler_arm64.h b/compiler/optimizing/scheduler_arm64.h
index 63d5b7d..e1a80ec 100644
--- a/compiler/optimizing/scheduler_arm64.h
+++ b/compiler/optimizing/scheduler_arm64.h
@@ -83,8 +83,8 @@
   M(SuspendCheck         , unused)                   \
   M(TypeConversion       , unused)                   \
   M(VecReplicateScalar   , unused)                   \
-  M(VecSetScalars        , unused)                   \
-  M(VecSumReduce         , unused)                   \
+  M(VecExtractScalar     , unused)                   \
+  M(VecReduce            , unused)                   \
   M(VecCnv               , unused)                   \
   M(VecNeg               , unused)                   \
   M(VecAbs               , unused)                   \
@@ -103,6 +103,7 @@
   M(VecShl               , unused)                   \
   M(VecShr               , unused)                   \
   M(VecUShr              , unused)                   \
+  M(VecSetScalars        , unused)                   \
   M(VecMultiplyAccumulate, unused)                   \
   M(VecLoad              , unused)                   \
   M(VecStore             , unused)