Make scalar_utils more visible

Internal: follow-up diff adds a custom op.

Differential Revision: [D77189188](https://our.internmc.facebook.com/intern/diff/D77189188/)

ghstack-source-id: 292207116
Pull Request resolved: #11862

Author: swolchok

kernels/portable/cpu/targets.bzl

@@ -72,8 +72,9 @@ def define_common_targets():
         srcs = [],
         exported_headers = ["scalar_utils.h", "selective_build.h"],
         visibility = [
-            "//executorch/kernels/portable/cpu/...",
+            "//executorch/kernels/fb/...",
             "//executorch/kernels/optimized/cpu/...",
+            "//executorch/kernels/portable/cpu/...",
             "//executorch/kernels/portable/test/...",
             "@EXECUTORCH_CLIENTS",
         ],