ARM: dts: imx6q-cm-fx6: fix the operation points

The current ldo settings of the cm-fx6 do not allow 1.2GHz cpu
frequency. At this frequency the module behaves unstable.

But the imx6q fuse indicates that 1.2GHz operation is possible.
Hence, remove the 1.2GHz operation point in the device tree.

Signed-off-by: Valentin Raevsky <valentin@compulab.co.il>
[christopher.spinrath@rwth-aachen.de: enhance commit message, adjust
 remaining operation points to match the ones in imx6q.dtsi and add
 a comment in the device tree]
Signed-off-by: Christopher Spinrath <christopher.spinrath@rwth-aachen.de>
Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>