stmmac: remove specific SoC Koption from platform.

This patch removes all the Koptions added to build the glue-logic files
for all different architectures: DWMAC_MESON, DWMAC_SUNXI, DWMAC_STI ...
Nowadays the stmmac needs to be compiled on several platforms; in some
case it very convenient to guarantee that its build is always completed
with success on all the branches where the driver is present.

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