MIPS: PM: Use struct syscore_ops instead of sysdevs for PM (v2)

Convert some MIPS architecture's code to using struct syscore_ops
objects for power management instead of sysdev classes and sysdevs.

This simplifies the code and reduces the kernel's memory footprint.
It also is necessary for removing sysdevs from the kernel entirely in
the future.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Acked-by: Greg Kroah-Hartman <gregkh@suse.de>
Acked-and-tested-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Cc: linux-kernel@vger.kernel.org
Cc: "Rafael J.  Wysocki" <rjw@sisk.pl>
Patchwork: http://patchwork.linux-mips.org/patch/2431/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>