BaseTools:The BOM character is processed when python reads a file

BaseTools:The BOM character is processed when python reads a file

When python3 reads an XML file it will parse the file in error
if the file has a BOM

Cc: Bob Feng <bob.c.feng@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Zhiju.Fan <zhijux.fan@intel.com>
Reviewed-by: Bob Feng <bob.c.feng@intel.com>