ARM: STi: DT: Enable mmc0 for both stih415 and stih416 SoCs

Because the first sdhci controller is present on both stih415 and
stih416 SoC which can both populate the b2020 board, it can be
enabled in the generic DT file.

Signed-off-by: Giuseppe Cavallaro <peppe.cavallaro@st.com>
Signed-off-by: Peter Griffin <peter.griffin@linaro.org>
Acked-by: Lee Jones <lee.jones@linaro.org>
Acked-by: Maxime Coquelin <maxime.coquelin@st.com>
Signed-off-by: Maxime Coquelin <maxime.coquelin@st.com>