cmsdk: add invalid input checking for persistent storage APIs

Some of this exists in the PersistentStorage implementation, but it
was never formally documented in the APIs.  Inherit the cmhw implementation
error checking & move it into the service.

Add tests to validate the new restrictions & a test that was previously
failing.

CYNGNOS-2237
Change-Id: I3ecda29fdd28bbc4e6d8ccce7511c4644065ea46