IntelFsp2Pkg/Tools: Add BSF bit field support in GenCfgOpt tool

IntelFsp2Pkg/Tools: Add BSF bit field support in GenCfgOpt tool

The current GenCfgOpt tool does not generate bit fields in BSF.
This change will allow bit fields to be created in BSF for a specific
FSP UPD item. The argument for the tool is also updated to be in sync
with the old usage model in IntelFspPkg.

Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Giri P Mudusuru <giri.p.mudusuru@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Maurice Ma <maurice.ma@intel.com>
Reviewed-by: Jiewen Yao <Jiewen.yao@intel.com>
Reviewed-by: Giri P Mudusuru <giri.p.mudusuru@intel.com>