ARM: dts: imx6sx: add phy-3p0-supply to usb phys

ARM: dts: imx6sx: add phy-3p0-supply to usb phys

The integrated usb phys are supplied by the 3p0 regulator, which has a
voltage range of 2.625V to 3.4V. Thus the min and max values are
corrected and the regulator added as a proper supply for the usb phys.

This fixes the following warnings during the probe of the mxs_phy
driver:

mxs_phy 20c9000.usbphy: supply phy-3p0 not found, using dummy regulator
mxs_phy 20ca000.usbphy: supply phy-3p0 not found, using dummy regulator

The regulator handling was introduced by commit `966d73152078 (usb: phy:
mxs: enable regulator phy-3p0 to improve signal qualilty, 2024-07-26)`.

Signed-off-by: Stefan Kerkmann <s.kerkmann@pengutronix.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>