ARM: dts: stm32: remove usbphyc ports vdda1v1 & vdda1v8 on stm32mp15 boards

vdda1v1 and vdda1v8 supplies are required by USB PLL, not by the PHYs.
Remove them from usbphyc child phy nodes now that they are managed in
usbphyc parent node at SoC level.

Cc: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Amelie Delaunay <amelie.delaunay@foss.st.com>
Tested-by: Marek Vasut <marex@denx.de>
Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>