[GlobalISel] translate freeze to new generic G_FREEZE

Summary:
As a follow up to https://reviews.llvm.org/D29014, add translation
support for freeze.

Introduce a new generic instruction G_FREEZE and translate freeze to it.

Reviewers: dsanders, aqjune, arsenm, aditya_nandakumar, t.p.northover, lebedev.ri, paquette, aemerson

Reviewed By: aqjune, arsenm

Subscribers: fhahn, lebedev.ri, wdng, rovka, hiraditya, jfb, volkan, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D77795