MdePkg/IndustryStandard: AEST Table definition
    
    Bugzilla: 3049 (https://bugzilla.tianocore.org/show_bug.cgi?id=3049)
    
    Add definition for the Arm Error Source Table (AEST) described in
    the ACPI for the Armv8 RAS Extensions 1.1 Platform Design Document,
    dated 28 September 2020.
    (https://developer.arm.com/documentation/den0085/0101/)
    
    Signed-off-by: Marc Moisson-Franckhauser <marc.moisson-franckhauser@arm.com>
    Signed-off-by: Sami Mujawar <sami.mujawar@arm.com>
    Reviewed-by: Liming Gao <gaoliming@byosoft.com.cn>
    Reviewed-by: Zhichao Gao <zhichao.gao@intel.com>