IntelFsp2Pkg: Add FSP 2.4 MultiPhase interface.

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=3916

Provide FSP 2.4 MultiPhase interface and scripts
support.

Cc: Nate DeSimone <nathaniel.l.desimone@intel.com>
Cc: Star Zeng <star.zeng@intel.com>
Signed-off-by: Chasel Chiu <chasel.chiu@intel.com>
Reviewed-by: Nate DeSimone <nathaniel.l.desimone@intel.com>

IntelFsp2Pkg/Include/Library/FspMultiPhaseLib.h

@@ -0,0 +1,55 @@
+/** @file
+  FSP MultiPhase Library.
+
+  Copyright (c) 2022, Intel Corporation. All rights reserved.<BR>
+  SPDX-License-Identifier: BSD-2-Clause-Patent
+
+**/
+
+#ifndef _FSP_MULTIPHASE_LIB_H_
+#define _FSP_MULTIPHASE_LIB_H_
+
+EFI_STATUS
+EFIAPI
+FspMultiPhaseSwitchStack (
+  );
+
+EFI_STATUS
+EFIAPI
+FspVariableRequestSwitchStack (
+  IN FSP_MULTI_PHASE_VARIABLE_REQUEST_INFO_PARAMS  *FspVariableRequestParams
+  );
+
+/**
+  This function handles FspMultiPhaseMemInitApi.
+
+  @param[in]  ApiIdx           Internal index of the FSP API.
+  @param[in]  ApiParam         Parameter of the FSP API.
+
+  @retval EFI_SUCCESS                 FSP execution was successful.
+  @retval EFI_INVALID_PARAMETER       Input parameters are invalid.
+  @retval EFI_UNSUPPORTED             The FSP calling conditions were not met.
+  @retval EFI_DEVICE_ERROR            FSP initialization failed.
+**/
+EFI_STATUS
+EFIAPI
+FspMultiPhaseMemInitApiHandler (
+  IN UINT32  ApiIdx,
+  IN VOID    *ApiParam
+  );
+
+/**
+  This function handles FspMultiPhaseSiInitApi.
+
+  @param[in]  ApiIdx           Internal index of the FSP API.
+  @param[in]  ApiParam         Parameter of the FSP API.
+
+**/
+EFI_STATUS
+EFIAPI
+FspMultiPhaseSiInitApiHandlerV2 (
+  IN UINT32  ApiIdx,
+  IN VOID    *ApiParam
+  );
+
+#endif