ARM: STi: DT: Add STiH407 family tsin3 pinctrl configuration

tsin3 channel can only be configured for serial data transfer.

On B2120 reference design tsin3 is brought out as TSB on the NIMB
slot of the B2004A daughter board.

Signed-off-by: Peter Griffin <peter.griffin@linaro.org>
Signed-off-by: Maxime Coquelin <maxime.coquelin@st.com>