vc/intel/edk2: Define FSP_SIG macro for FSP 2.x compatibility

This patch introduces the FSP_SIG macro into EDK2 headers to ensure
compilation compatibility when using FSP 2.x specifications.

Previously, the macro was only defined for FSP 1.1.

BUG=b:242829490
TEST=Successful build of google/rex0 with 64-bit FSP.

Change-Id: I4f97fc303ca2881ccd17b4d149d01c3b671dbbde
Signed-off-by: Subrata Banik <subratabanik@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/81622
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-by: Varshit Pandya <pandyavarshit@gmail.com>
Reviewed-by: Ronak Kanabar <ronak.kanabar@intel.com>

src/vendorcode/intel/edk2/UDK2017/IntelFsp2Pkg/Include/Guid/FspHeaderFile.h

@@ -30,6 +30,8 @@
 
 #define FSP_INFO_HEADER_SIGNATURE  SIGNATURE_32 ('F', 'S', 'P', 'H')
 
+#define FSP_SIG         0x48505346      /* 'FSPH' */
+
 #pragma pack(1)
 
 ///

src/vendorcode/intel/edk2/edk2-stable202005/IntelFsp2Pkg/Include/Guid/FspHeaderFile.h

@@ -24,6 +24,8 @@
 
 #define FSP_INFO_HEADER_SIGNATURE  SIGNATURE_32 ('F', 'S', 'P', 'H')
 
+#define FSP_SIG         0x48505346      /* 'FSPH' */
+
 #pragma pack(1)
 
 ///

src/vendorcode/intel/edk2/edk2-stable202111/IntelFsp2Pkg/Include/Guid/FspHeaderFile.h

@@ -24,6 +24,8 @@
 
 #define FSP_INFO_HEADER_SIGNATURE  SIGNATURE_32 ('F', 'S', 'P', 'H')
 
+#define FSP_SIG         0x48505346      /* 'FSPH' */
+
 #pragma pack(1)
 
 ///

src/vendorcode/intel/edk2/edk2-stable202302/IntelFsp2Pkg/Include/Guid/FspHeaderFile.h

@@ -32,6 +32,8 @@
 #define FSP_IA32                               0
 #define FSP_X64                                1
 
+#define FSP_SIG         0x48505346      /* 'FSPH' */
+
   #pragma pack(1)
 
 ///