doc: remove incorrect limitation on QAT PMD

QAT supports authentication only operations,
for any authentication algorithm (such as SHA1-HMAC),
as long as it is supported by QAT, so it means
that it is not necessary to create a chained operation
in order to use these algorithms.

Fixes: 1703e94ac5ce ("qat: add driver for QuickAssist devices")
CC: stable@dpdk.org
Signed-off-by: Pablo de Lara <pablo.de.lara.guarch@intel.com>
Acked-by: Fiona Trahe <fiona.trahe@intel.com>
Acked-by: Declan Doherty <declan.doherty@intel.com>