ARM: dts: sun4i: fix device node ordering

This patch changes the device node position of ps20 and ps21 to fix
ordering by rising physical address.

From

uart7: serial@01c29c00
i2c0: i2c@01c2ac00
i2c1: i2c@01c2b000
i2c2: i2c@01c2b400
ps20: ps2@01c2a000
ps21: ps2@01c2a400

to

uart7: serial@01c29c00
ps20: ps2@01c2a000
ps21: ps2@01c2a400
i2c0: i2c@01c2ac00
i2c1: i2c@01c2b000
i2c2: i2c@01c2b400

Signed-off-by: Patrick Menschel <menschel.p@posteo.de>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>