arm64: dts: mediatek: mt8516: rename usb phy

The USB phy node is named usb0_phy but there is only one phy with
2 ports on MT8516. Rename the phy to make it more obvious it can
also support the usb1 node.
The usb1 node will be added in a follow-up commit.

Signed-off-by: Fabien Parent <fparent@baylibre.com>
Link: https://lore.kernel.org/r/20201014162404.1312544-1-fparent@baylibre.com


Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>