lmkd: Introduce liblmkd_utils for communicating with lmkd process

A number of tools and tests require communication with lmkd.
In order to avoid code duplication liblmkd_utils implements
functions commonly used when interacting with lmkd process.
Isolate communication protocol details into lmkd.h

Bug: 63631020

Change-Id: Id840983d55b7db60013d52dee0c3187943811822
Signed-off-by: Suren Baghdasaryan <surenb@google.com>