BaseTools tools_def.txt: Remove -P option in GCC ASLPP_FLAGS

BaseTools tools_def.txt: Remove -P option in GCC ASLPP_FLAGS

https://bugzilla.tianocore.org/show_bug.cgi?id=227

After -P option is removed, the generated preprocessed ASL file will have
line markers. The extra information can be removed by Trim script. ASL code
can refer to the definition in C source file. This has been supported in
VS and XCODE tool chains.

Cc: Yonghong Zhu <yonghong.zhu@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Liming Gao <liming.gao@intel.com>
Reviewed-by: Yonghong Zhu <yonghong.zhu@intel.com>