[Executorch] Handle broadcast semantics for last dim (#6602)

Pull Request resolved: https://github.com/pytorch/executorch/pull/6521

This diff add support to handle element wise mul op when broadcast is across
last dim
ghstack-source-id: 251185496
@exported-using-ghexport

Differential Revision: [D64156863](https://our.internmc.facebook.com/intern/diff/D64156863/)

Co-authored-by: Kimish Patel <kimishpatel@fb.com>