stmmac: make ioaddr 'void __iomem *' rather than unsigned long

This avoids unnecessary casting and adds the ioaddr in the
private structure.
This patch also removes many warning when compile the driver.

Signed-off-by: Giuseppe Cavallaro <peppe.cavallaro@st.com>
Signed-off-by: David S. Miller <davem@davemloft.net>