[ET-VK][ez] Implement rsqrt (#6472)

Pull Request resolved: https://github.com/pytorch/executorch/pull/6456

TSIA. This op is used in Llama model architecture.
ghstack-source-id: 249709740
@exported-using-ghexport

Differential Revision: [D64840505](https://our.internmc.facebook.com/intern/diff/D64840505/)

Co-authored-by: Stephen Jia <ssjia@meta.com>