dt-bindings: phy: phy-stm32-usbphyc: move PLL supplies to parent node

PLL block requires to be powered with 1v1 and 1v8 supplies to catch ENABLE
signal.
Currently, supplies are managed through phy_ops .power_on/off, and PLL
activation/deactivation is managed through phy_ops .init/exit.
The sequence of phy_ops .power_on/.phy_init, .power_off/.exit is USB
drivers dependent.
To ensure a good behavior of the PLL, supplies have to be managed at PLL
activation/deactivation. That means the supplies need to be put in usbphyc
parent node and not in phy children nodes.

Signed-off-by: Amelie Delaunay <amelie.delaunay@foss.st.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20210105090525.23164-2-amelie.delaunay@foss.st.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>