ARM: dts: sunxi: h3/h5: Add r_i2c pinmux node

H3/H5 SoCs contain an I2C controller optionally available
on the PL0 and PL1 pins. This patch adds pinmux configuration
for this controller.

Signed-off-by: Ondrej Jirman <megous@megous.com>
[Icenowy: change commit message, node name and function name]
Signed-off-by: Icenowy Zheng <icenowy@aosc.io>
Reviewed-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Chen-Yu Tsai <wens@csie.org>