ARM: STi: DT: Add STiH407 family tsin5 pinctrl configuration

tsin5 can only be configured for serial data transfer. However
depending on board design, two alternate tsin5 pin configurations
are available, both in pin-controller-front0.

pinctrl_tsin5_serial_alt1 is brought out on B2120 reference
design as TSD on 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>