Add two patterns to remove unused zlow.stick and zlow.unstick operations

[tungld]

ZLow operations are side-effect so they are not removed automatically if unused.

This patch adds two canonicalization patterns to remove zlow.stick and zlow.unstick operations, which has been seen in some models.

Patterns for the other zlow operations will be added on demand, as needed.

[AlexandreEichenberger]

Confused, why would a stick with only one use be removed?

[tungld]

For example:

func.func @remove_unused_stick_op(%arg0: memref<5x10xf32>) -> memref<10xf32> {
  %0 = memref.alloc() {alignment = 4096 : i64} : memref<5x10xf16, #map>
  "zlow.stick"(%arg0, %0) {layout = "2D"} : (memref<5x10xf32>, memref<5x10xf16, #map>) -> ()
  %1 = memref.alloc() {alignment = 4096 : i64} : memref<10xf32>
  return %1: memref<10xf32>
}

The result %0 of zlow.stick has only one use (that is zlow.stick), so zlow_stick can be removed.