arm64: dts: allwinner: a64: add R_I2C controller

Allwinner A64 has a I2C controller, which is in the R_ MMIO zone and has
two groups of pinmuxes on PL bank, so it's called R_I2C.

Add support for this I2C controller and the pinmux which doesn't conflict
with RSB.

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