arm64: dts: marvell: fix USB3 regulator definition on MacchiatoBin

Due to the lack of GPIO support, the USB3 regulator definition was
left unfinished in the MacchiatoBin DT description. Now that GPIO
support is available, this commit adjusts the Device Tree to properly
describe the USB3 regulator.

[gregory.clement@free-electrons.com: use commit log from Thomas]

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>