dracut: add "--check=crc32" to xz compression

dracut: add "--check=crc32" to xz compression

As mentioned in kernel/Documentation/xz.txt:

...
Notes on compression options

  Since the XZ Embedded supports only streams with no integrity check
  or CRC32, make sure that you don't use some other integrity check
  type when encoding files that are supposed to be decoded by the
  kernel. With liblzma, you need to use either LZMA_CHECK_NONE or
  LZMA_CHECK_CRC32 when encoding. With the xz command line tool, use
  --check=none or --check=crc32.

  Using CRC32 is strongly recommended unless there is some other layer
  which will verify the integrity of the uncompressed data anyway.
...