UefiCpuPkg/CpuDxe: consider freed-memory guard in non-stop mode

UefiCpuPkg/CpuDxe: consider freed-memory guard in non-stop mode

Non-stop mode was introduced / explained in commit 8f2613628acf
("MdeModulePkg/MdeModulePkg.dec: add new settings for PCDs",
2018-08-30).

The macro HEAP_GUARD_NONSTOP_MODE was added to CpuDxe in commit
dcc026217fdc ("UefiCpuPkg/CpuDxe: implement non-stop mode for uefi",
2018-08-30).

Another instance of the macro HEAP_GUARD_NONSTOP_MODE was added to
PiSmmCpuDxeSmm -- with BIT1|BIT0 replaced with BIT3|BIT2 -- in commit
09afd9a42a7f ("UefiCpuPkg/PiSmmCpuDxeSmm: implement non-stop mode for
SMM", 2018-08-30)

Since the freed-memory guard is for UEFI-only. This patch only updates
HEAP_GUARD_NONSTOP_MODE in "UefiCpuPkg/CpuDxe/CpuDxe.h" (add BIT4).

Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Star Zeng <star.zeng@intel.com>
Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Ruiyu Ni <ruiyu.ni@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Jian J Wang <jian.j.wang@intel.com>
Reviewed-by: Eric Dong <eric.dong@intel.com>