qed: simplify initialization of the chains with an external PBL

Fill PBL table parameters for chains with an external PBL data earlier on
qed_chain_init_params() rather than on allocation itself. This simplifies
allocation code and allows to extend struct ext_pbl for other chain types.

Signed-off-by: Alexander Lobakin <alobakin@marvell.com>
Signed-off-by: Igor Russkikh <irusskikh@marvell.com>
Signed-off-by: Michal Kalderon <michal.kalderon@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>