If IOMMU is enabled, the legacy BIOS need allow the legacy memory
access by the legacy device.
The legacy memory is below 1M memory and HighPmm memory.
Cc: Star Zeng <star.zeng@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Jiewen Yao <jiewen.yao@intel.com>
Reviewed-by: Star Zeng <star.zeng@intel.com>