crypto/qat: make the session struct variable in size

crypto/qat: make the session struct variable in size

This patch changes the qat firmware session data structure from a fixed
size to a variable size which is dependent on the size of the chosen
algorithm.
This reduces the amount of bytes which are transferred across
PCIe and thus helps to increase qat performance when the
accelerator is bound by PCIe.

Signed-off-by: John Griffin <john.griffin@intel.com>
Acked-by: Fiona Trahe <fiona.trahe@intel.com>