ARM / SA1100: Use struct syscore_ops for "core" power management

Replace the sysdev class and struct sys_device used for power
management by the SA1100 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>