GenCfgOpt.py: remove tailing space from output file

GenCfgOpt.py: remove tailing space from output file

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=1212

UPD header files generated by GenCfgOpt.py may have
tailing white space from some of the UPD description in DSC,
especially when python script automatically switching lines
for long description string. This patch will always remove
tailing white space for UPD header files.

Test: Verified the patch can remove tailing space in
      output header files when UPD DSC contains intentional
      tailing white space.

Cc: Jiewen Yao <Jiewen.yao@intel.com>
Cc: Gao Liming <liming.gao@intel.com>
Cc: Zhu Yonghong <yonghong.zhu@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Chasel Chiu <chasel.chiu@intel.com>
Reviewed-by: Jiewen Yao <Jiewen.yao@intel.com>