f2fs utils: Add mkf2fsuserimg.sh and make_f2fs

This is used to generate empty userdata.img files.
Normally, "fastboot format userdata" should be used.

Caveats:
 - It only builds an empty sparse image.
 - windows/mac unsupported

Change-Id: I5fbd9724fdd3f4513e7c91f123fc5fffcb475012
Signed-off-by: JP Abgrall <jpa@google.com>
3 files changed