bnx2x: Minor code improvements

Minor code improvements
Small changes to make the code a little bit more efficient and mostly
more readable:
- Using unified macros for EMAC_RD/WR which looks like normal REG_RD/WR
- Removing the NIG_WR since it did nothing and was only confusing
- On bnx2x_panic_dump, print only the used parts of the rings
- define parameters only on the branch they are needed and not at the
  beginning of the function
- using NETIF_MSG_INTR and not private BNX2X_MSG_SP for debug prints

Signed-off-by: Eilon Greenstein <eilong@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>