arm64: dts: imx8mn: Update VDD_ARM 1.2GHz setpoint voltage

arm64: dts: imx8mn: Update VDD_ARM 1.2GHz setpoint voltage

The latest datasheet Rev. 0.1, 03/2020 removes below constrain:

"If VDD_SOC/GPU/DDR = 0.95V, then VDD_ARM must be >= 0.95V."

So, for 1.2GHz setpoint VDD_ARM can use its typical voltage
directly.

The datasheet can be downloaded from below link:
https://www.nxp.com/docs/en/data-sheet/IMX8MNCEC.pdf

Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>