arm64: dts: zii-ultra: add PCIe PHY supply

The ZII Ultra board uses the same design as the EVK board supplying
PCIE_VPH with 3.3V. Add this connection to the DT to allow the PCIe
driver to enable the internal PHY regulator, as required by the
reference manual.

Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Reviewed-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>