IMemory: add unsecurePointer

pointer -> unsecurePointer has happened in internal master. In order for
AOSP clients to be able to use the new API, adding it here.

Test: code builds
Change-Id: Ie280f48b9c338bf667c5d83867b78fb4fef49264
Merged-In: If8474d0c6a2f0a23cb0514eac1a86c71e334fcc9