arm64: allwinner: h6: add R_I2C controller

Allwinner H6 SoC has a R_I2C controller wired to the PL0/PL1 pins, which
are used in the reference design to connect AXP805 PMIC.

Add support for it.

Signed-off-by: Icenowy Zheng <icenowy@aosc.io>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>