bnxt_en: Add IRQ remapping logic.

Add remapping logic so that bnxt_en can use any arbitrary MSIX vectors.
This will allow the driver to reserve one range of MSIX vectors to be
used by both bnxt_en and bnxt_re.  bnxt_en can now skip over the MSIX
vectors used by bnxt_re.

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