UefiCpuPkg/MpInitLib: force flushing TLB for AP in mwait loop mode
    
    The reason doing this is that we found that calling StartupAllAps() to
    flush TLB for all APs in CpuDxe driver after changing page attributes
    will spend a lot of time to complete. If there are many page attributes
    update requests, the whole system performance will be slowed down
    explicitly, including any shell command and UI operation.
    
    The solution is removing the flush operation for AP in CpuDxe driver.
    Since TLB is always flushed in HLT loop mode, we just need to enforce
    a TLB flush for mwait loop mode.
    
    Cc: Ruiyu Ni <ruiyu.ni@intel.com>
    Cc: Jiewen Yao <jiewen.yao@intel.com>
    Cc: Eric Dong <eric.dong@intel.com>
    Cc: Laszlo Ersek <lersek@redhat.com>
    Contributed-under: TianoCore Contribution Agreement 1.1
    Signed-off-by: Jian J Wang <jian.j.wang@intel.com>
    Reviewed-by: Ruiyu Ni <ruiyu.ni@intel.com>