arm64: dts: allwinner: h6: enable AXP805 PMIC on Pine H64

Pine H64 board has an AXP805 PMIC on it, wired up in standalone, or
self-working, mode.

Enable it in the device tree.

Signed-off-by: Icenowy Zheng <icenowy@aosc.io>
Reviewed-by: Icenowy Zheng <icenowy@aosc.io>
Tested-by: Icenowy Zheng <icenowy@aosc.io>
Acked-by: Maxime Ripard <maxime.ripard@bootlin.com>
Signed-off-by: Chen-Yu Tsai <wens@csie.org>