Add the ISurfaceComposer::createGraphicBuffer IPC.

This change adds a new binder method to the ISurfaceComposer interface.
This IPC is intended to allow SurfaceFlinger clients to allocate gralloc
buffers using SurfaceFlinger as a proxy to gralloc.

Change-Id: Ide9fc283aec5da6268ba62cfed0c3319a50b640d