bnxt_en: Add doorbell information to bnxt_en_dev struct.

The purpose of this is to inform the RDMA driver the size of the doorbell
BAR that the L2 driver has mapped and the portion that is mapped
uncacheable.  The unchaeable portion is shared with the RoCE driver.
Any remaining unmapped doorbell BAR can be used by the RDMA driver for
its own purpose.  Currently, the entire L2 portion is mapped uncacheable.

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