ARM: sun8i: v3s: add LRADC device node

Allwinner V3s features a LRADC like the ones in older SoCs.

Add a device tree node for it.

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