[AArch64][GISel] Expand coverage of FAdd and FSub.

This adds some more extensive test coverage for fadd/fsub through global isel,
switching the opcodes to use the more complete ActionDefinitions to handle more
cases.
diff --git a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
index 4b059f3..cd08bf2 100644
--- a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
@@ -4831,6 +4831,7 @@
   case TargetOpcode::G_SUB:
   case TargetOpcode::G_MUL:
   case TargetOpcode::G_FADD:
+  case TargetOpcode::G_FSUB:
   case TargetOpcode::G_FMUL:
   case TargetOpcode::G_UADDSAT:
   case TargetOpcode::G_USUBSAT: