net,marvell: Add dependency on HAS_IOMEM

On archs like S390 or um this driver cannot build nor work.
Make it depend on HAS_IOMEM to bypass build failures.

drivers/built-in.o: In function `orion_mdio_probe':
drivers/net/ethernet/marvell/mvmdio.c:228: undefined reference to `devm_ioremap'
Signed-off-by: NRichard Weinberger <richard@nod.at>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/marvell/Kconfig

@@ -33,6 +33,7 @@ config MV643XX_ETH
 
 config MVMDIO
 	tristate "Marvell MDIO interface support"
+	depends on HAS_IOMEM
 	select PHYLIB
 	---help---
 	  This driver supports the MDIO interface found in the network