crypto: qat - remove unused members in suof structure

Remove the members `css_key` and `css_signature` which are not used for
doing the firmware authentication.

The signed image pointer can be calculated using the pointer to the CSS
header and the length of the CSS header, making these members redundant.

Signed-off-by: Jack Xu <jack.xu@intel.com>
Reviewed-by: Ahsan Atta <ahsan.atta@intel.com>
Reviewed-by: Giovanni Cabiddu <giovanni.cabiddu@intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Giovanni Cabiddu <giovanni.cabiddu@intel.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>