ARM: dts: berlin: add I2C nodes for BG2Q

The Marvell Berlin BG2Q has 4 TWSI compatible with the Synopsys
DesignWare I2C driver. Add the corresponding nodes.

The pin-muxing setup is also done here, since there cannot be another
muxing setup if I2C{0,1,2,3} are enabled.

Signed-off-by: Antoine Ténart <antoine.tenart@free-electrons.com>
Signed-off-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>