[mlir][bufferization] Implement BufferDeallocationopInterface for scf.forall.in_parallel

The scf.forall.in_parallel terminator operation has a nested graph region with
the NoTerminator trait. Such regions are not supported by the default
implementations. Therefore, this commit adds a specialized implementation for
this operation which only covers the case where the nested region is empty.
This is because after bufferization, ops like tensor.parallel_insert_slice were
already converted to memref operations residing int the scf.forall only and the
nested region of scf.forall.in_parallel ends up empty.

Reviewed By: springerm

Differential Revision: https://reviews.llvm.org/D158979