intel_idle: do not sprinkle module parameter definitions around

This is a cleanup which improves code consistency. Move the force_irq_on
module parameter variable and definition to the same place where we have
variables and definitions for other module parameters.

Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Reviewed-by: Zhang Rui <rui.zhang@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>