ARM: dts: renesas: Fix USB PHY device and child node names

make dtbs_check:

    usb-phy@e6590100: '#phy-cells' is a required property
	    From schema: dtschema/schemas/phy/phy-provider.yaml

The R-Car Gen2 USB PHY device nodes do not represent USB PHYs
theirselves, and thus do not have "#phy-cells" properties.  Fix the
warning by renaming them from "usb-phy" to "usb-phy-controller".
Rename their child nodes from "usb-channel" to "usb-phy", as these do
represent USB PHYs.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Link: https://lore.kernel.org/r/6442b4042e26537abc8632c4772f8201685f1f1f.1663165098.git.geert+renesas@glider.be