ARM: dts: BCM5301X: use non-deprecated USB 2.0 PHY binding

The new binding covers a single reg and uses syscon to reference shared
register.

References: 55b9b741 ("dt-bindings: phy: brcm,ns-usb2-phy: bind just a PHY block")
Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>