[PATCH] bnx2: add 5708 support

Add 5708 copper and serdes basic support, including 2.5 Gbps support
on 5708 serdes. SPEED_2500 is also added to ethtool.h

Signed-off-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>