ARM: sun8i: v40: add 5V regulator for Banana Pi M2 Berry

On the Banana Pi M2 Berry board, the 5V power output (used by HDMI, SATA
and USB) is controlled via a GPIO.

Add regulator node for it.

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