extract_files: Add support for treble compatible makefiles

To be honest, this name is a little misleading, this is how it should
have been done in the first place. This allows devices to copy vendor
files to the proper location depending on TARGET_COPY_OUT_VENDOR rather
than hardcoding system/vendor. This allows devices with dedicated vendor
partitions to copy directly to vendor. The only reason it's optional
is that some nexi set TARGET_COPY_OUT_VENDOR to system which would cause
some weird breakage.

Change-Id: Ic46bc1086737835340abef9f61693d386bc6a5dc