drivers/net/ethernet/marvell/Kconfig: Let PXA168_ETH depend on HAS_IOMEM

drivers/net/ethernet/marvell/Kconfig: Let PXA168_ETH depend on HAS_IOMEM

PXA168_ETH need HAS_IOMEM, so depend on it, the related error (with
allmodconfig under um):

    CC [M]  drivers/net/ethernet/marvell/pxa168_eth.o
  drivers/net/ethernet/marvell/pxa168_eth.c: In function ‘pxa168_eth_probe’:
  drivers/net/ethernet/marvell/pxa168_eth.c:1605:2: error: implicit declaration of function ‘iounmap’ [-Werror=implicit-function-declaration]
    iounmap(pep->base);
    ^

Signed-off-by: Chen Gang <gang.chen.5i5j@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>