[AMDGPU] Enable divergence driven ISel for ADD/SUB i64

Summary:
Currently we custom select add/sub with carry out to scalar form relying on later replacing them to vector form if necessary.
This change enables custom selection code to take the divergence of adde/addc SDNodes into account and select the appropriate form in one step.

Reviewers: arsenm, vpykhtin, rampitec

Reviewed By: arsenm, vpykhtin

Subscribers: kzhuravl, jvesely, wdng, nhaehnle, yaxunl, dstuttard, tpr, t-tye, hiraditya, kerbowa

Differential Revision: https://reviews.llvm.org/D76371