arm64: dts: imx8mp-phycore-som: Update regulator output voltages

Set the regulator voltages to the min and max values the i.MX8MP
requires and not what the PMIC provides.

Signed-off-by: Teresa Remmet <t.remmet@phytec.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>