cpufreq: imx-cpufreq-dt: Fix no OPPs available on unfused parts

Early samples without fuses written report "0 0" which means consumer
segment and minimum speed grading. According to datasheet the minimum speed
grade is not supported for consumer parts so all OPPs are disabled
which results in stack dumps later on.

Fix by clamping minimum consumer speed grade to 1 on imx8mm and imx8mq.

Fixes: 4d28ba1d ("cpufreq: Add imx-cpufreq-dt driver")

Signed-off-by: Leonard Crestez <leonard.crestez@nxp.com>
[ Viresh: s/minumum/minimum/ in patch and log ]
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>