BaseTools: Move OverrideAttribs to OptRomInfStatement.py

Move "class OverrideAttribs" to OptRomInfStatement.py to remove
"import OptionRom" which may form a circular import:
GenFds.OptionRom => GenFds.OptRomInfStatement => GenFds.OptionRom

Contributed-under: TianoCore Contribution Agreement 1.1
Cc: Yonghong Zhu <yonghong.zhu@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Signed-off-by: Gary Lin <glin@suse.com>
Reviewed-by: Jaben Carsey <jaben.carsey@intel.com>

BaseTools/Source/Python/GenFds/FdfParser.py

@@ -4493,7 +4493,7 @@ class FdfParser:
     #
     def __GetOptRomOverrides(self, Obj):
         if self.__IsToken('{'):
-            Overrides = OptionRom.OverrideAttribs()
+            Overrides = OptRomInfStatement.OverrideAttribs()
             while True:
                 if self.__IsKeyword( "PCI_VENDOR_ID"):
                     if not self.__IsToken( "="):

BaseTools/Source/Python/GenFds/OptRomInfStatement.py

@@ -45,9 +45,8 @@ class OptRomInfStatement (FfsInfStatement):
     #   @param  self        The object pointer
     #
     def __GetOptRomParams(self):
-        from . import OptionRom
         if self.OverrideAttribs is None:
-            self.OverrideAttribs = OptionRom.OverrideAttribs()
+            self.OverrideAttribs = OverrideAttribs()
 
         if self.OverrideAttribs.NeedCompress is None:
             self.OverrideAttribs.NeedCompress = self.OptRomDefs.get ('PCI_COMPRESS')
@@ -150,3 +149,17 @@ class OptRomInfStatement (FfsInfStatement):
                     OutputFileList.extend(FileList)
 
         return OutputFileList
+
+class OverrideAttribs:
+
+    ## The constructor
+    #
+    #   @param  self        The object pointer
+    #
+    def __init__(self):
+
+        self.PciVendorId = None
+        self.PciClassCode = None
+        self.PciDeviceId = None
+        self.PciRevision = None
+        self.NeedCompress = None