intel_idle: replace conditionals with static_cpu_has(X86_FEATURE_ARAT)

If the 'arat' cpu flag is set, then the conditionals in intel_idle() that
guard calling tick_broadcast_enter()/exit() will never be true. Use
static_cpu_has(X86_FEATURE_ARAT) to create a fast path to replace
the conditional.

Signed-off-by: Jason Baron <jbaron@akamai.com>
Acked-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>