Filter out include DSC files in ConfigEditor open dialog

In ConfigEditor, when open DSC files, many files will show up. It
is expected to only open the CfgDataDef.dsc. This patch changed
the file match pattern to only list *Def.dsc file.  In this way,
user will not make mistake to open some include DSC file.

Signed-off-by: Maurice Ma <maurice.ma@intel.com>

BootloaderCorePkg/Tools/ConfigEditor.py

@@ -448,7 +448,7 @@ class Application(Frame):
 
         if Type == 'dsc':
             FileType = 'DSC or PKL'
-            FileExt  = 'dsc *.pkl'
+            FileExt  = 'pkl *Def.dsc'
         else:
             FileType = Type.upper()
             FileExt  = Type