AppPkg/Applications/Python: Add support for the pyexpat module.

AppPkg/Applications/Python: Add support for the pyexpat module.

Add required flags to [BuildOptions] in PythonCore.inf.
Add initialization routine to Efi/config.c.
Alter #include targets if building for UEFI in expat_external.h and xmlparse.c.
Add expat modifications to PyMod-2.7.2/Modules/expat.

Contributed-under: TianoCore Contribution Agreement 1.0
Submitted-by:   Duane Voth <duanev@gmail.com>
Signed-off-by:  daryl.mcdaniel@intel.com
Reviewed-by:    duanev@gmail.com
Reviewed-by:    daryl.mcdaniel@intel.com
git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@14071 6f19259b-4bc3-4df7-8a09-765794883524