ARM: dts: STi: Fix pinconf setup for STiH416 serial2

This patch fixes a bug in pinctrl setup of serial2 device, Some of the
pins in the pinctrl node of serial2 do not belong to that
pin-controller. This patch divides them in the pins into there
respective pin controller nodes.

Without this patch serial on StiH416-B2000 Board will not work as it
fails with:

"st-pinctrl pin-controller-rear.3: failed to get pin(99) name
st-pinctrl pin-controller-rear.3: maps: function serial2 group serial2-0
num 4
pinconfig core: failed to register map default (3): no group/pin given"

Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@st.com>
Signed-off-by: Olof Johansson <olof@lixom.net>