x86: Make offlined CPU enter deepest C state

x86: Make offlined CPU enter deepest C state

Before cpuidle is introduced, offlined CPU only enter C1 (by HLT
instruction). This is not optimal since C2/C3 can bring more power
saving. Since now cpuidle is introduced, it is time for offlined CPU
to enter more deeper C state.

This patch add the logic to make offlined CPU enter deepest C state,
if cpuidle is enabled.

Signed-off-by: Yu Ke <ke.yu@intel.com>
Signed-off-by: Wei Gang <gang.wei@intel.com>
Signed-off-by: Tian Kevin <kevin.tian@intel.com>