ctf: isolate the abstraction of memory map byte-buffer.

ctf: isolate the abstraction of memory map byte-buffer.

The concept of the memory map mechanism should not be exposed
outside the StreamInput. This is internal to StreamInput.
The API should exposed : give me a byte buffer (I don't care how).

Change-Id: I832d2776845a07173f4ef7cb47fd9c75c7db73bf
Signed-off-by: Etienne Bergeron <etienne.bergeron@gmail.com>
Reviewed-on: https://git.eclipse.org/r/19652
IP-Clean: Matthew Khouzam <matthew.khouzam@ericsson.com>
Tested-by: Hudson CI
Reviewed-by: Matthew Khouzam <matthew.khouzam@ericsson.com>