Provide interface for in memory bspatch.

Renamed existing MemoryFile to BufferFile, and added a read only
MemoryFile to provide file interface to read file data already in
memory without extra copy (extra memory usage).

Added write only SinkFile to provide sink function support used in
applypatch. It will enable imgpatch the ability to stream output.

Test: mma
Bug: 26982501

Change-Id: I025ce4064c9f46623dd73f24d30e21e88f08a292