[MLIR][Transform] Consolidate the transform ops of get_parent_for and loop unroll...

[MLIR][Transform] Consolidate the transform ops of get_parent_for and loop unroll from affine and scf dialects.

This patch consolidates the two transform ops from the affine dialect
and the scf dialect to avoid code duplication.

This is to address the review comments from
https://reviews.llvm.org/D137997.

The transform ops directory / file structure for the affine dialect is
kept for the purpose of forth-coming transform ops
for affine, but get_parent_for and unroll are removed.

Reviewed By: nicolasvasilache

Differential Revision: https://reviews.llvm.org/D138980