ACPI: Use syscore_ops instead of sysdev class and sysdev

ACPI uses a sysdev class and a sysdev for executing
irqrouter_resume() before turning on interrupts on the boot CPU.
However, since irqrouter_resume() ignores its argument, the entire
mechanism may be replaced with a struct syscore_ops object which
is considerably simpler.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Signed-off-by: Len Brown <len.brown@intel.com>