Rename frameworks to differ between kernels and backends. (#3484)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/3484
overriding_review_checks_triggers_an_audit_and_retroactive_review
Oncall Short Name: executorch

Reviewed By: mergennachin

Differential Revision: D56868690

fbshipit-source-id: 9df756473f4a83b63a844ca2c95f2051598203f9