RDMA/bnxt_re: Avoid creating fence MR for newer adapters

Limit the usage of fence MR to adapters older than Gen P5 products.

Fixes: 1801d87b ("RDMA/bnxt_re: Support new 5760X P7 devices")
Signed-off-by: Kashyap Desai <kashyap.desai@broadcom.com>
Signed-off-by: Bhargava Chenna Marreddy <bhargava.marreddy@broadcom.com>
Signed-off-by: Kalesh AP <kalesh-anakkur.purayil@broadcom.com>
Signed-off-by: Selvin Xavier <selvin.xavier@broadcom.com>
Link: https://lore.kernel.org/r/1705985677-15551-2-git-send-email-selvin.xavier@broadcom.com


Signed-off-by: Leon Romanovsky <leon@kernel.org>