drivers/net/stmmac/: add HAS_IOMEM dependency

The stmmac driver does not compile on s390:

drivers/net/stmmac/stmmac_main.c: In function 'stmmac_adjust_link':
drivers/net/stmmac/stmmac_main.c:210: error: implicit declaration of function 'readl'
drivers/net/stmmac/stmmac_main.c:263: error: implicit declaration of function 'writel'
drivers/net/stmmac/stmmac_main.c: In function 'stmmac_dvr_probe':
drivers/net/stmmac/stmmac_main.c:1674: error: implicit declaration of function 'ioremap'
drivers/net/stmmac/stmmac_main.c:1674: warning: assignment makes pointer from integer without a cast
drivers/net/stmmac/stmmac_main.c:1761: error: implicit declaration of function 'iounmap'
make[3]: *** [drivers/net/stmmac/stmmac_main.o] Error 1

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Giuseppe CAVALLARO <peppe.cavallaro@st.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: David S. Miller <davem@davemloft.net>