init: add a swapoff built-in command

Enables a method for swapping off certain block devices or files. This
will be used before hibernation occurs.

Bug: 339688542
Test: Manual, verified that calling swapoff from a init file swapsoff
location that is specified

Change-Id: I212a6f303a023c3e440b557caae82ad3904ac9c9
2 files changed