[BNX2]: Support NVRAM on 5709.

The NVRAM interface is slightly modified on the 5709.  To properly
support it, we need to change the buffered flag in the flash data
structure into multiple flags to indicate buffered operation, address
translation, and the use of write enable (WREN).  The 5709 flash
only requires the buffered operation bit to be set.

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