arm64: dts: renesas: Revise usb2_phy nodes and phys properties

Since the commit 233da2c9 ("dt-bindings: phy: rcar-gen3-phy-usb2:
Revise #phy-cells property") revised the #phy-cells, this patch follows
the updated document for R-Car Gen3 and RZ/A2 SoCs.

Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>