image_types.bbclass: replace genext2fs with populate-extfs.sh

image_types.bbclass: replace genext2fs with populate-extfs.sh

* The benefits:
  - Really support ext4

  - Support the sparse file (we lost the sparse file in the image in the
    past, the sparse file became into the common file)

  - Fix the error reported by fsck: (ext2/ext3)
      Inode 1025, i_size is 16384, should be 17408.

  - Have a uniform code for ext2/3/4 generation

* Comments from Darren Hart:
Basically, genext2fs doesn't support creating ext4 filesystems. It
creates, as I understand it, an ext2 filesystem, then adds a journal,
and sets some bits. It can't support the newer features like extents. So
what we end up with is a bit of a hack for a filesystem.

The ext tools (e2fsprogs) unfortunately don't provide an integrated
solution for generating prepopulated filesystem images as many other
mkfs* tools do. One thing missing was symlink support in libext2fs. I
added that support and demonstrated a script which uses the e2fsprogs
debugfs tool that can populate the newly formatted filesystem from a
directory and without root privileges.

[YOCTO #3848]

(From OE-Core rev: 40c3e18f43b2f074cec97d21aeb8d21f26dd5048)

Signed-off-by: Robert Yang <liezhi.yang@windriver.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>