BaseTools: Use absolute import in GenFds

BaseTools: Use absolute import in GenFds

Based on "futurize -f libfuturize.fixes.fix_absolute_import"

Since circular import is not allowed after adopting absolute import, the
following changes are applied to break the circles.

* BaseTools/Source/Python/GenFds/Capsule.py
  - Delay "from .GenFds import GenFds" until GenCapsule()
  - Delay "from .GenFds import FindExtendTool" until GenFmpCapsule()
  To break the circle:
  AutoGen.AutoGen => GenFds.FdfParser => GenFds.Capsule => GenFds.GenFds =>
  GenFds.FdfParser

* BaseTools/Source/Python/GenFds/Fd.py
  - Delay "from .GenFds import GenFds" until GenFd()
  To break the circle:
  AutoGen.AutoGen => GenFds.FdfParser => GenFds.Fd => GenFds.GenFds =>
  GenFds.FdfParser

* BaseTools/Source/Python/GenFds/Fv.py
  - Delay "from .GenFds import GenFds" until AddToBuffer()
  To break the circle:
  AutoGen.AutoGen => GenFds.FdfParser => GenFds.Fd => GenFds.Fv =>
  GenFds.GenFds => GenFds.FdfParser

* BaseTools/Source/Python/GenFds/GuidSection.py
  - Delay "from .GenFds import FindExtendTool" until GuidSection()
  To break the circle:
  AutoGen.AutoGen => GenFds.FdfParser => GenFds.Fd => GenFds.Fv =>
  GenFds.AprioriSection => GenFds.FfsFileStatement => GenFds.GuidSection =>
  GenFds.GenFds => GenFds.FdfParser

* BaseTools/Source/Python/GenFds/OptRomInfStatement.py
  - Delay "from . import OptionRom" until __GetOptRomParams()
  To break the circle:
  AutoGen.AutoGen => GenFds.FdfParser => GenFds.OptionRom =>
  GenFds.OptRomInfStatement => GenFds.OptionRom

* BaseTools/Source/Python/GenFds/OptionRom.py
  - Remove the unused "from GenFds import GenFds"
  To break the circle:
  AutoGen.AutoGen => GenFds.FdfParser => GenFds.OptionRom =>
  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>