Update on "[Executorch] Renable operator optimization flags"

Previous attempt at this resulted in revert due to app size increase. Much of
this was due to op_div exploding. Two diffs underneath solve this issue

Differential Revision: [D65606666](https://our.internmc.facebook.com/intern/diff/D65606666/)

[ghstack-poisoned]

Author: kimishpatel

shim/xplat/executorch/kernels/portable/op_registration_util.bzl

@@ -1285,4 +1285,4 @@ def portable_source_list():
 
 def portable_header_list():
     """All the header file names from //executorch/kernels/portable/cpu/"""
-    return ["selective_build.h", "scalar_utils.h", "math_constants.h", "vec_ops.h"]
+    return ["selective_build.h", "scalar_utils.h", "math_constants.h", "vec_ops.h", "op_div_impl.h"]