bnxt_en: Workaround Nitro A0 hardware RX bug (part 2).

The hardware is unable to drop rx packets not matching the RX filters.  To
workaround it, we create a special VNIC and configure the hardware to
direct all packets not matching the filters to it.  We then setup the
driver to drop packets received on this VNIC.

This patch creates the infrastructure for this VNIC, reserves a
completion ring, and rx rings.  Only shared completion ring mode is
supported.  The next 2 patches add a NAPI to handle packets from this
VNIC and the setup of the VNIC.

Signed-off-by: Prashant Sreedharan <prashant.sreedharan@broadcom.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>