bnx2x: Fix BCM57810-KR AN speed transition

BCM57810-KR link may not come up in 1G after running loopback test, so set
the relevant registers to their default values before starting KR autoneg.

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