ARM: dts: uniphier: add NAND pinmux node

This commit adds pin-mux nodes for the NAND controller.
Some SoCs support 2 chip selects and the others only support
1 chip select.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>