MdeModulePkg DxeCore: Enhance MemoryAttributesTable installation

MdeModulePkg DxeCore: Enhance MemoryAttributesTable installation

Current MemoryAttributesTable will be installed on ReadyToBoot event
at TPL_NOTIFY level, it maybe incorrect when PcdHiiOsRuntimeSupport
= TRUE as HiiDatabaseDxe will have runtime memory allocation for HII
OS runtime support on and after ReadyToBoot. The issue was exposed at
http://article.gmane.org/gmane.comp.bios.edk2.devel/10125.

To make sure the correctness of MemoryAttributesTable, this patch is
to enhance MemoryAttributesTable installation to install
MemoryAttributesTable on ReadyToBoot event at TPL_CALLBACK - 1 level
to make sure it is at the last of ReadyToBoot event, and also hook
runtime memory allocation after ReadyToBoot.

Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Cc: Feng Tian <feng.tian@intel.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Star Zeng <star.zeng@intel.com>
Reviewed-by: Jiewen Yao <jiewen.yao@intel.com>