[GlobalISel][AArch64] Legalize vector G_FPOW

This instruction is legalized in the same way as G_FSIN, G_FCOS, G_FLOG10, etc.

Update legalize-pow.mir and arm64-vfloatintrinsics.ll to reflect the change.

Differential Revision: https://reviews.llvm.org/D60218

llvm-svn: 358764
diff --git a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
index f983b02..e5c73f6 100644
--- a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
@@ -1318,6 +1318,7 @@
   case TargetOpcode::G_FSQRT:
   case TargetOpcode::G_FEXP:
   case TargetOpcode::G_FEXP2:
+  case TargetOpcode::G_FPOW:
     assert(TypeIdx == 0);
     Observer.changingInstr(MI);