ARM: sunxi: dt: Add A10 UARTs to the dtsi.

The Allwinner A10 SoC has 8 available UARTs, which is 6 more than on the
A13, so add the missing UARTs to the sun4i-a10 dtsi.

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