net: ks8851: Remove ks8851_mll.c

The ks8851_mll.c is replaced by ks8851_par.c, which is using common code
from ks8851.c, just like ks8851_spi.c . Remove this old ad-hoc driver.
Signed-off-by: Marek Vasut <marex@denx.de>
Cc: David S. Miller <davem@davemloft.net>
Cc: Lukas Wunner <lukas@wunner.de>
Cc: Petr Stetiar <ynezz@true.cz>
Cc: YueHaibing <yuehaibing@huawei.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>