intel_idle: fix confusing message

By default, all non-POLL C-states are entered with interrupts disabled.

There are 2 ways to make 'intel_idle' enter C-states with interrupts
enabled:
  1. Mark the C-state with the CPUIDLE_FLAG_IRQ_ENABLE flag.
  2. Use the force_irq_on module parameter.

The former is the "proper" way of doing it, it is per-C-state and
per-platform. The latter is for debugging purposes only.

The problem is that intel_idle prints the "forced intel_idle_irq"
message in both cases, even though the former case does not needed
this message, because nothing is forced there. This patch addresses the
problem.

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>