bnxt_en: Add support for updating flash more securely

To support Secure Firmware Update, we must be able to allocate
a staging area in the Flash.  This patch adds support for the
"update" type to tell firmware to do that.

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