libdm: Add DeleteDeviceDeferred API

This can be useful in case when a device mapper device can't be deleted
straight away, and instead delete needs to be enqueued until last
reference to the device is closed.

Bug: 187864524
Bug: 188713178
Test: atest libdm_test
Change-Id: Ie8a130baa54e6e16d8d159389bd760bf873eca40