net:stmmac: convert driver to use devm_request_and_ioremap.

This patch moves calls to ioremap and request_mem_region to
devm_request_and_ioremap call.

Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@st.com>
Signed-off-by: David S. Miller <davem@davemloft.net>