stmmac: code tidy-up

This patch tidies up the code. I have run Linden (and verified with checkpatch)
many part of the driver trying to reorganize some sections respecting the
codying-style rules in the points where it was not done.

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