BaseTools: Move ImageBinDict to GenFdsGlobalVariable.py

BaseTools: Move ImageBinDict to GenFdsGlobalVariable.py

Move "ImageBinDict" from GenFds.py to GenFdsGlobalVariable.py so that we
can remove the requirement to import GenFds.GenFds in Capsule.py, Fd.py and
Fv.py. This breaks the following circular imports:

* GenFds.FdfParser => GenFds.Capsule => GenFds.GenFds => GenFds.FdfParser
* GenFds.FdfParser => GenFds.Fd => GenFds.GenFds => GenFds.FdfParser
* GenFds.FdfParser => GenFds.Fd => GenFds.Fv => GenFds.GenFds =>
  GenFds.FdfParser

Contributed-under: TianoCore Contribution Agreement 1.1
Cc: Yonghong Zhu <yonghong.zhu@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Signed-off-by: Gary Lin <glin@suse.com>
Reviewed-by: Jaben Carsey <jaben.carsey@intel.com>