BaseTools: Enhance FV info report file path to support absolute path

BaseTools: Enhance FV info report file path to support absolute path

When generate build report, Tool will get the info like size, Fv Name,
etc from the xx.Fv.txt file and add these info into the build report.
This patch support the xx.Fv.txt to use absolute file path format since
user may provide specified FV path.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Yonghong Zhu <yonghong.zhu@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>