MdeModulePkg/Core/Dxe: Add EndOfDxe workaround for NULL pointer detection

MdeModulePkg/Core/Dxe: Add EndOfDxe workaround for NULL pointer detection

One of issue caused by enabling NULL pointer detection is that some PCI
device OptionROM, binary drivers and binary OS boot loaders may have NULL
pointer access bugs, which will prevent BIOS from booting and is almost
impossible to fix. BIT7 of PCD PcdNullPointerDetectionPropertyMask is used
as a workaround to indicate BIOS to disable NULL pointer detection right
after event gEfiEndOfDxeEventGroupGuid, and then let boot continue.

Cc: Star Zeng <star.zeng@intel.com>
Cc: Eric Dong <eric.dong@intel.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Michael Kinney <michael.d.kinney@intel.com>
Cc: Ayellet Wolman <ayellet.wolman@intel.com>
Suggested-by: Ayellet Wolman <ayellet.wolman@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: Jiewen Yao <jiewen.yao@intel.com>