ARM / Integrator: Use struct syscore_ops for core PM

Replace the sysdev class and struct sys_device used for power
management by the Integrator interrupt-handling code with a
struct syscore_ops object which is simpler.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Acked-by: Greg Kroah-Hartman <gregkh@suse.de>