bnx2: Remove config access to non-standard registers

In KVM passthrough mode, the driver may not have config access to
non-standard registers.  The BNX2_PCICFG_MISC_CONFIG config register
access to setup mailbox swapping can be done using MMIO.

Update version to 2.0.20.

Signed-off-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>