[mlir] StdToLLVM: Add error when the sourceMemRef of a subview is not a llvm type.

A memref_cast casting to a memref with a non identity map can't be
lowered to llvm. Take the following case:

```

func @invalid_memref_cast(%arg0: memref<?x?xf64>) {
  %c1 = constant 1 : index
  %c0 = constant 0 : index
  %5 = memref_cast %arg0 : memref<?x?xf64> to memref<?x?xf64, #map1>
  %25 = std.subview %5[%c0, %c0][%c1, %c1][] : memref<?x?xf64, #map1> to memref<?x?xf64, #map1>
  return
}
```

When lowering the subview mlir was assuming `%5` to have an llvm type
(which is not the case as mlir failed to lower the memref_cast).

Differential Revision: https://reviews.llvm.org/D74466