arm64: dts: imx8mn-evk: update vdd_soc dvs voltage

Per schematic, BUCK1 is for VDD_SOC&DRAM&PU_0V9. The nxp,dvs-run-voltage
and nxp,dvs-standby-voltage need set for BUCK1, not BUCK2.
BUCK2 is for A53, which is handled by DVFS, so no need dvs property.
nxp,dvs-run-voltage is not needed, since bootloader must configure
voltage to make system boot well.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Acked-by: Marco Felsch <m.felsch@pengutronix.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>