net: ks8851: Split out SPI specific code from probe() and remove()

Factor out common code into ks8851_probe_common() and
ks8851_remove_common() to permit both SPI and parallel
bus driver variants to use the common code path for
both probing and removal.

There should be no functional change.

Reviewed-by: Andrew Lunn <andrew@lunn.ch>
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>
Signed-off-by: David S. Miller <davem@davemloft.net>