x86,mrst: Power control commands update

On the Intel MID devices SCU commands are issued to manage power
off and the like. We need to issue different ones for
non-Lincroft based devices.

Signed-off-by: Alek Du <alek.du@intel.com>
Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>