Refactoring of NoPE (#3840)

Summary:
Pull Request resolved: #3840

X-link: facebookresearch/FBGEMM#927

Some of the refactoring for iRope w/ quantized KV [D69486380] didn't go into the commited version. This diff reflects the changes of the accepted version.

Reviewed By: GD06

Differential Revision: D71324793

fbshipit-source-id: 29cfbc122e3a601da33087cbde9738e08dfb3cfe

Author: Aya-ZIbra