[mlir][llvm] Use tablegen to import atomic ops from LLVM IR.

[mlir][llvm] Use tablegen to import atomic ops from LLVM IR.

The revision imports the atomic operations using
tablegen generated builders. Additionally, it moves their tests to
the instructions.ll test file.

Depends on D135880

Reviewed By: ftynse

Differential Revision: https://reviews.llvm.org/D135944