arm64: dts: imx8mm-kontron: Make sure SOC and DRAM supply voltages are correct

It looks like the voltages for the SOC and DRAM supply weren't properly
validated before. The datasheet and uboot-imx code tells us that VDD_SOC
should be 800 mV in suspend and 850 mV in run mode. VDD_DRAM should be
950 mV for DDR clock frequencies of up to 1.5 GHz.

Let's fix these values to make sure the voltages are within the required
range.

Fixes: 8668d8b2

 ("arm64: dts: Add the Kontron i.MX8M Mini SoMs and baseboards")
Cc: stable@vger.kernel.org
Signed-off-by: Frieder Schrempf <frieder.schrempf@kontron.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>