ARM: dts: dove: Add internal i2c multiplexer node

This adds a i2c-mux-pinctrl node to dove.dtsi for the internal i2c
mux found on Dove SoCs. Up to now, we had no board using any of the
two additional i2c busses, so make sure the change does not break
any existing boards.

Therefore, we rename the i2c-controller node label to "i2c" and
enable it by default. Also, the dedicated sub-bus (now "i2c0") is
enabled by default. The two optional sub-busses require additional
external pin-muxing, so disable them by default.

Signed-off-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Acked-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>