ARM: sunxi: dt: Move uart0 to sun4i-a10.dtsi

The UART0 is only available on the Allwinner A10 SoCs, and not on the
A13, so move the uart0 node to sun4i-a10.dtsi.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Acked-by: Emilio López <emilio@elopez.com.ar>
Tested-by: Emilio López <emilio@elopez.com.ar>