MdePkg: Add ACPI 5.1 table definition for WAET

This is a struct needed for virtualizing Windows.

https://uefi.org/acpi entry for WAET links to
https://learn.microsoft.com/en-us/previous-versions/gg487524(v=msdn.10)

which describes the 32-bit flags field with bits 0 and 1 defined.

Signed-off-by: Dionna Glaze <dionnaglaze@google.com>

MdePkg/Include/IndustryStandard/Acpi51.h

@@ -1834,6 +1834,25 @@ typedef struct {
   UINT32    EntryCount;
 } EFI_ACPI_5_1_EINJ_TRIGGER_ACTION_TABLE;
 
+///
+/// Windows ACPI Emulated devices Table
+///
+typedef struct {
+  EFI_ACPI_DESCRIPTION_HEADER    Header;
+  ///
+  /// Container of a bitmask of Windows behavior that this system requires
+  /// Bit 0 - RTC good
+  /// Bit 1 - ACPI PM timer good
+  ///
+  UINT32                         EmulatedDeviceFlags;
+} EFI_ACPI_5_1_WAET_TABLE;
+
+///
+/// WAET Flags. All other bits are reserved and must be 0.
+///
+#define EFI_ACPI_5_1_WAET_FLAGS_RTC_GOOD            BIT0
+#define EFI_ACPI_5_1_WAET_FLAGS_ACPI_PM_TIMER_GOOD  BIT1
+
 ///
 /// Platform Communications Channel Table (PCCT)
 ///