SPE MFC proxy command functions

This set of functions provides PPE-initiated DMA functionality (see Cell Broadband Engine Architecture, MFC Proxy Commands) through the usage of the SPE MFC Proxy Command Issue facility. Main threads can use these functions to move data to and from an SPE local store area.
Note: The naming of the commands is based on a SPE centric view, for example, "put" means a transfer from the SPE local store to an effective address valid in the main thread.