PM: Remove legacy PM

AFAICT pm_send_all is a nop when noone uses pm_register...

Hmm.. can we just force CONFIG_PM_LEGACY=n, and see what happens?

Or maybe this is better idea? It may break build somewhere, but it
should be easy to fix... (it builds here, i386 and x86-64).

Signed-off-by: Pavel Machek <pavel@suse.cz>
Acked-by: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Signed-off-by: Len Brown <len.brown@intel.com>