Allow sign_target_files_apks.py to create zip64 signed TF.zip.

We should only disallow zip64 for the image and OTA zips (because we
don't have zip64 support in libziparchive yet). But target_files zips
are fine to use zip64 with host tools (and we already do that in
add_img_to_target_files.py).

This CL also sets the default compression method to DEFLATED when
creating the signed TF.zip.

Test: sign_target_files.apks.py signing a large TF.zip passes.
Change-Id: I8043739860604134fa1166e920c95c28797bbcc1