arm64: dts: imx8mp-skov: operate CPU at 850 mV by default

arm64: dts: imx8mp-skov: operate CPU at 850 mV by default

The Skov i.MX8MP boards are passively cooled and heatsink is specced for
continuous operation at 1.2 GHz only. Short bouts of 1.6 GHz are ok,
but these should be invoked intentionally, not as part of
suspend/resume cycles.

Therefore, configure RUN frequency as 850 mV and remove the higher
voltage operating points from those permissible for suspend.

Fixes: 6d382d51d979 ("arm64: dts: freescale: Add SKOV IMX8MP CPU revB board")
Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>