The maximum CPU frequency for the i.MX53 QSB is 1GHz, so disable the
1.2GHz OPP. This makes the board work again with configs that have
cpufreq enabled like imx_v6_v7_defconfig on which the board stopped
working with the addition of cpufreq-dt support.

Fixes: 791f4166 ("ARM: dts: imx53: add cpufreq-dt support")
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>