[POWERPC] PS3: System manager support

Add PS3 system manager support and the ppc_md routines restart() and
power_off().

The system manager provides an event notification mechanism for reporting
events like thermal alert and button presses.  It also provides support to
control system shutdown and startup.

Signed-off-by: Geoff Levand <geoffrey.levand@am.sony.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>