[flang][openacc] Add basic lowering to new data operations for acc.enter_data

This is an initial patch that lowers acc.enter_data copyin/create/attach
clauses to the newly added data operand operations. Follow up patches will
add support for array section and derived type and derived type component
as well as support in other data operation.

Reviewed By: razvanlupusoru

Differential Revision: https://reviews.llvm.org/D148721