ARM: STi: STiH407: Add spi default pinctrl groups.

Now we have default pinconfig groups for each SPI
controller ensure it is used by the SPI controller
node.

Acked-by: Lee Jones <lee.jones@linaro.org>
Acked-by: Patrice Chotard <patrice.chotard@st.com>
Signed-off-by: Peter Griffin <peter.griffin@linaro.org>
Signed-off-by: Maxime Coquelin <maxime.coquelin@st.com>