ARM: sunxi: dt: Fix aliases

Commit f77d55a3 ("serial: 8250_dw: get index of serial line from DT
aliases") made the serial driver now use the serial aliases to get the tty
number, pointing out that our aliases have been wrong all along.

Remove them from the DTSI and add custom ones in the relevant boards.

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