The implementation of MdeModulePkg\Universal\Acpi\AcpiTableDxe reserves
first entry of RSDT/XSDT to FADT, the first entry value is 0 when FADT
is not installed. So the RSDT/XSDT parsing code should check the entry
value first before checking the table signature.
Cc: Jiewen Yao <jiewen.yao@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1 Signed-off-by: Star Zeng <star.zeng@intel.com> Reviewed-by: Jiewen Yao <jiewen.yao@intel.com>