ARM: dts: UniPhier: add on-chip UART device nodes

The UniPhier on-chip UART driver was merged into the mainline by
commit 1a8d2903 ("serial: 8250_uniphier: add UniPhier serial
driver").

Add device nodes to make it really available.

We no longer have to depend on the on-board UART device (16550A),
so let's change the chosen and aliases to point to the on-chip ones.
Also, turn on the on-board Ethernet device.

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