arm64: dts: imx8mp: use 800MHz NoC OPP for nominal drive mode

When running in nominal drive mode, the maximum allowed frequency for
the NoC is 800MHz, but the OPP table for the i.MX8MP interconnect device
listed the 1GHz operating point for the NoC, regardless of the active
mode.

The newly introduced imx8mp-nominal.dtsi header reconfigures the clock
controller to observe nominal drive mode limits, so have it modify the
maximum NoC OPP as well.

Fixes: 255fbd9e ("arm64: dts: imx8mp: Add optional nominal drive mode DTSI")
Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>