bnx2x: Support loading cnic resources at run-time

This patch replaces the BCM_CNIC define with a flag which can change at run-time
and which does not use the CONFIG_CNIC kconfig option.
For the PF/hypervisor driver cnic is always supported, however allocation of
cnic resources and configuration of the HW for offload mode is done only when
the cnic module registers bnx2x.

Signed-off-by: Merav Sicron <meravs@broadcom.com>
Signed-off-by: Dmitry Kravkov <dmitry@broadcom.com>
Signed-off-by: Eilon Greenstein <eilong@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>