Allwinner A64 have a RSB controller like the one on A23/A33 SoCs.

Add it and its pinmux.
Signed-off-by: Icenowy Zheng <icenowy@aosc.io>
Acked-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>