ARM64: dts: marvell: armada-37xx: Add USB2 node

Armada 37xx SoC embedded an EHCI controller. This patch adds the device
tree node enabling its support.

Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>