[mlir] Add MemoryEffects::Allocate to memref::CloneOp

Without it BufferDeallocationPass process only CloneOps created during pass itself and ignore all CloneOps that were already present in IR.

For our specific usecase:

```
func @dealloc_existing_clones(%arg0: memref<?x?xf64>, %arg1: memref<?x?xf64>) -> memref<?x?xf64> {
  return %arg0 : memref<?x?xf64>
}
```

Input arguments will be freed immediately after return from function and we want to prolong lifetime for the returned argument.
To achieve this we explicitly add clones to all input memrefs and expect that BufferDeallocationPass will add correct deallocs to them (unnessesary clone+dealloc pairs will be canonicalized away later).

Differential Revision: https://reviews.llvm.org/D104973