bnx2x: Create bnx2x_cmn.* files

Newly created files have no functionality changes,
but includes some functionality from bnx2x_main.c which
is common for PF and coming in the future VF driver.

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