ARM: dts: sun8i-a33: Add pinmux setting for uart0 on PB pins

The A33 adds an additional pinmux option for uart0 on the PB pins.
This was not present on the A23. Nor is it available on the H3,
which does not have the PB pingroup.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>