UefiCpuPkg/MpInitLib: Disable interrupt at ExitBootServices AP Mwait

UefiCpuPkg/MpInitLib: Disable interrupt at ExitBootServices AP Mwait

Within function ApWakeupFunction():

When source level debugger is enabled, AP interrupts will be enabled by
EnableDebugAgent(). Then the AP function will be executed by:

Procedure (Parameter);

After the AP function returns, AP interrupts will be disabled when the
APs are placed in loop mode (both HltLoop and MwaiLoop).

However, at ExitBootServices, ApWakeupFunction() is called with
'Procedure' equals to RelocateApLoop().

(ExitBootServices callback registered within InitMpGlobalData())

RelocateApLoop() never returns, so it has to disable the AP interrupts by
itself. However, we find that interrupts are only disabled for the
HltLoop case, but not for the MwaitLoop case (within file MpFuncs.nasm).

This commit adds the missing disabling of AP interrupts for MwaitLoop.

Also, for X64, this commit will disable the interrupts before switching to
32-bit mode.

Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Jian J Wang <jian.j.wang@intel.com>
Cc: Star Zeng <star.zeng@intel.com>
Cc: Eric Dong <eric.dong@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Hao Wu <hao.a.wu@intel.com>
Reviewed-by: Ruiyu Ni <ruiyu.ni@intel.com>
Reviewed-by: Jiewen Yao <jiewen.yao@intel.com>
Reviewed-by: Jeff Fan <vanjeff_919@hotmail.com>