ARM: dts: imx53-ppd: Rename usbphy nodes

This renames usbphy nodes 2 & 3, so that they follow the same
format as usbphy node 0 & 1 from imx53.dtsi.

Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.co.uk>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>