stmmac: extend mac addr reg and fix perfect filering

This patch is to extend the number of MAC address registers
for 16 to 32. In fact, other new 16 registers are available in new
chips and this can help on perfect filter mode for unicast.

This patch also fixes the perfect filtering mode by setting the
bit 31 in the MAC address registers.

v2: fixed Coding Style.

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