net: lan743x: select CRC16

lan743x now fails to build when CONFIG_CRC16 is disabled:

drivers/net/ethernet/microchip/lan743x_main.o: In function crc16'

Force it on like all other users do.

Fixes: 4d94282a ("lan743x: Add power management support")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: David S. Miller <davem@davemloft.net>