ARM: dts: UniPhier: add UART and USB pinmux nodes

The DT nodes in uniphier-pinctrl.dtsi provide the default pinctrl
settings that would be suitable for most boards.  You can still
override them in your board DTS file if necessary.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Olof Johansson <olof@lixom.net>