cpufreq: imx6q: check speed grades for i.MX6ULL

Check the max speed supported from the fuses for i.MX6ULL and update the
operating points table accordingly.

Signed-off-by: Sébastien Szymanski <sebastien.szymanski@armadeus.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Tested-by: Stefan Agner <stefan@agner.ch>
Reviewed-by: Stefan Agner <stefan@agner.ch>
Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>
Acked-by: Shawn Guo <shawnguo@kernel.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>