powerpc/powernv: reboot when requested by firmware

powerpc/powernv: reboot when requested by firmware

Use orderly_reboot so userspace will to shut itself down via the reboot
path.  This is required for graceful reboot initiated by the BMC, such as
when a user uses ipmitool to issue a 'chassis power cycle' command.

Signed-off-by: Joel Stanley <[email protected]>
Acked-by: Michael Ellerman <[email protected]>
Cc: Fabian Frederick <[email protected]>
Cc: Benjamin Herrenschmidt <[email protected]>
Cc: Rusty Russell <[email protected]>
Cc: Jeremy Kerr <[email protected]>
Cc: David S. Miller <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>