BaseTools/BinToPcd: --offset must be 8-byte aligned

BaseTools/BinToPcd: --offset must be 8-byte aligned

https://bugzilla.tianocore.org/show_bug.cgi?id=974
https://bugzilla.tianocore.org/show_bug.cgi?id=965

Update help to state that --offset must be 8-byte aligned.
Verify that --offset is 8-byte aligned and print an error
message if it is not 8-byte aligned.

Cc: Yanyan Sun <yanyan.sun@intel.com>
Cc: Yonghong Zhu <yonghong.zhu@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Signed-off-by: Michael D Kinney <michael.d.kinney@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Reviewed-by: Yonghong Zhu <yonghong.zhu@intel.com>