[mlir][llvm] Add atomic support to the StoreOp.

This revision adds atomic support to the StoreOp. It chooses
to print the atomic keywords together with the syncscope and
ordering arguments. The revision also implements verifiers to
ensure the constraints that apply to atomic store operations
are checked.

Depends on D144112

Reviewed By: Dinistro

Differential Revision: https://reviews.llvm.org/D144200