[mlir] Printing oilist element

[mlir] Printing oilist element

This patch attempts to deduce when the oilist element must be printed
based on the optional arguments to it. This especially helps creating
an operation accurately because with the current implementation, the
inferred unit attributes must be manually added to print the clauses
appropriately.

Reviewed By: Mogball

Differential Revision: https://reviews.llvm.org/D121579