crypto/qat: improve security instance setup

crypto/qat: improve security instance setup

This patch makes some improvements to the security instance setup for
the QAT SYM PMD, as follows:
- fix potential memory leak where the security instance was not freed if
  an error occurred later in the device creation
- tidy-up security instance initialization code by moving it all,
  including enabling the RTE_CRYPTODEV_FF_SECURITY feature, into one
  '#ifdef RTE_LIBRTE_SECURITY' block

Fixes: 6f0ef237404b ("crypto/qat: support DOCSIS protocol")

Signed-off-by: David Coyle <david.coyle@intel.com>
Acked-by: Fiona Trahe <fiona.trahe@intel.com>