BaseTools: Fix the bug use same FMP_PAYLOAD in different capsule file

Fix the bug that use same FMP_PAYLOAD in different capsule file. Because
in previous FMP generation, the FMP already be generated, so we don't
need to regenerate again.

Cc: Liming Gao <liming.gao@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Yonghong Zhu <yonghong.zhu@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>
(cherry picked from commit d4c558e83d)

BaseTools/Source/Python/GenFds/CapsuleData.py

@@ -183,6 +183,8 @@ class CapsulePayload(CapsuleData):
         self.VendorCodeFile = []
         self.Certificate_Guid = None
         self.MonotonicCount = None
+        self.Existed = False
+        self.Buffer = None
 
     def GenCapsuleSubItem(self, AuthData=[]):
         if not self.Version:
@@ -239,4 +241,5 @@ class CapsulePayload(CapsuleData):
             VendorFile = open(self.VendorCodeFile, 'rb')
             Buffer += VendorFile.read()
             VendorFile.close()
+        self.Existed = True
         return Buffer