ARM: sun5i: Add a DTSI common to A10s and A13

The A10s and the A13 are very similar SoCs, the only difference being the
number of pins and the number of devices available (number of UARTs, EMAC only
in the A10s, etc.), and the clocks and pinctrl functions obviously.

Create a common DTSI that will be included by the A10s and A13 DTSI, that will
add their SoC differences in there.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>