stmmac: fix kconfig for crc32 build error

stmmac uses crc32 functions so it needs to select CRC32.

Fixes build error:
drivers/built-in.o: In function `dwmac1000_set_filter':
dwmac1000_core.c:(.text+0x3c380): undefined reference to `crc32_le'
dwmac1000_core.c:(.text+0x3c384): undefined reference to `bitrev32'

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