crypto: qat - add fw_counters debugfs file

Expose FW counters statistics by providing the "fw_counters" file
under debugfs. Currently the statistics include the number of
requests sent to the FW and the number of responses received
from the FW for each Acceleration Engine, for all the QAT product
line.

This patch is based on earlier work done by Marco Chiappero.

Co-developed-by: Adam Guerin <adam.guerin@intel.com>
Signed-off-by: Adam Guerin <adam.guerin@intel.com>
Signed-off-by: Lucas Segarra Fernandez <lucas.segarra.fernandez@intel.com>
Reviewed-by: Giovanni Cabiddu <giovanni.cabiddu@intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>