MdeModulePkg/DxeIpl: support more NX related PCDs

MdeModulePkg/DxeIpl: support more NX related PCDs

BZ#1116: https://bugzilla.tianocore.org/show_bug.cgi?id=1116

Currently IA32_EFER.NXE is only set against PcdSetNxForStack. This
confuses developers because following two other PCDs also need NXE
to be set, but actually not.

    PcdDxeNxMemoryProtectionPolicy
    PcdImageProtectionPolicy

This patch solves this issue by adding logic to enable IA32_EFER.NXE
if any of those PCDs have anything enabled.

Cc: Star Zeng <star.zeng@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Ruiyu Ni <ruiyu.ni@intel.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Jian J Wang <jian.j.wang@intel.com>
Reviewed-by: Star Zeng <star.zeng@intel.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>