IntelSiliconPkg/VtdInfo: Add Null Root Entry Table PPI

Null root entry table address is a fixed silicon reserved address,
which is used to block the DMA transfer.

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=2867



Change-Id: I3aa2b2e7a11e0327857c6ed9bc92cd209d3ade9d
Cc: Ray Ni <ray.ni@intel.com>
Cc: Rangasai V Chaganty <rangasai.v.chaganty@intel.com>
Signed-off-by: Sheng Wei <w.sheng@intel.com>
Reviewed-by: Ray Ni <ray.ni@intel.com>
Reviewed-by: Jenny Huang <jenny.huang@intel.com>
Reviewed-by: Jiewen Yao <Jiewen.yao@intel.com>