ARM: dts: sun9i: optimus: Switch to phy core regulator bindings for usb phys

Since the phy core already supports specifying a regulator to handle
during power up/down, it was decided to drop the regulator support
in the sun9i usb phy driver.

This patch switches the DT to the core bindings. This and the phy driver
would be in the same release and should not be a problem as far as DT
stability goes.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Acked-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>