powerpc: add Freescale hypervisor partition control functions

Add functions to restart and halt the current partition when running under
the Freescale hypervisor.  These functions should be assigned to various
function pointers of the ppc_md structure during the .probe() function for
the board:

	ppc_md.restart = fsl_hv_restart;
	ppc_md.power_off = fsl_hv_halt;
	ppc_md.halt = fsl_hv_halt;

Signed-off-by: Timur Tabi <timur@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>