Allow several system property files
Allow several system property files

TARGET_SYSTEM_PROP now is a list of files and all of them
are included in the build.prop.

Change-Id: I494f86412b0a299ee4c066e49ab4f4686bc2178a

xorware/android_build,xorware/android_build,xorware/android_build,xorware/android_build,xorware/android_build