[MemInit] Use new MemInit API.

The system property will only disable heap memory initialization. If you
want to disable MTE (which I don't think was the subject of the original
patch), you can use the MTE sysprops: 'arm64.memtag.process.<pname> =
"off"'.

Bug: 135772972
Test: Device boots.
Change-Id: I180be76ff2f776f1ec1a607de848ff6c81da852d