BaseTools: Enhance BaseTools supports FixedAtBuild usage in VFR file

BaseTools: Enhance BaseTools supports FixedAtBuild usage in VFR file

This patch is to update BaseTools generate Fixed PCD APIs and Value into
$(MODULE_NAME)StrDefs.h for VFR only. If the module has VFR files, and it
directly consumes FixedAtBuild PCD, BaseTool will generate those
FixedAtBuild PCD value into its $(MODULE_NAME)StrDefs.h. FixedPcdGetXX
macro are always generated. Every FixedPcd _PCD_VALUE_PcdName will be
generated without the postfix U or UL or ULL.

Fixes: https://bugzilla.tianocore.org/show_bug.cgi?id=348
Cc: Liming Gao <liming.gao@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Yonghong Zhu <yonghong.zhu@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>