BaseTools:Fix GenFds issue for BuildOption replace GenFdsOption

BZ:https://bugzilla.tianocore.org/show_bug.cgi?id=2455

BuildOption is used by TargetTxtClassObj.py
GenFdsOption is used by GenFds.py
When the GenFds tool is used alone (e.g. python3 -m GenFds.GenFds -h)
With the OptionParser function, the first detected function
prints the help message

import TargetTxtClassObj to GenFds,
The BuildOption will be executed and replace GenFdsOption

We removed all objects associated with this problem that
were created directly during the import process
(e.g. BuildOption, BuildTarget = MyOptionParser(),
 TargetTxt = TargetTxtDict())

The Patch is going to fix this issue

Signed-off-by: Zhiju.Fan <zhijux.fan@intel.com>

Cc: Liming Gao <liming.gao@intel.com>
Cc: Bob Feng <bob.c.feng@intel.com>
Reviewed-by: Bob Feng <bob.c.feng@intel.com>

BaseTools/Source/Python/GenFds/GenFds.py

@@ -20,7 +20,7 @@ from linecache import getlines
 from io import BytesIO
 
 import Common.LongFilePathOs as os
-from Common.TargetTxtClassObject import TargetTxt
+from Common.TargetTxtClassObject import TargetTxtDict
 from Common.DataType import *
 import Common.GlobalData as GlobalData
 from Common import EdkLogger
@@ -210,6 +210,8 @@ def GenFdsApi(FdsCommandDict, WorkSpaceDataBase=None):
         BuildConfigurationFile = os.path.normpath(os.path.join(ConfDirectoryPath, "target.txt"))
         if os.path.isfile(BuildConfigurationFile) == True:
             # if no build target given in command line, get it from target.txt
+            TargetObj = TargetTxtDict()
+            TargetTxt = TargetObj.Target
             if not GenFdsGlobalVariable.TargetName:
                 BuildTargetList = TargetTxt.TargetTxtDictionary[TAB_TAT_DEFINES_TARGET]
                 if len(BuildTargetList) != 1: