ARM: dts: imx6ull: add operating points

i.MX6ULL has different operating ranges than i.MX6UL so add the
operating points for the i.MX6ULL and remove them from board device
trees. A 25mV offset is added to the minimum allowed values like for the
i.MX6UL.
The valid frequencies are now selected by the cpufreq driver according
to ratings stored in fuses since commit 0aa9abd4 ("cpufreq: imx6q:
check speed grades for i.MX6ULL")

Signed-off-by: Sébastien Szymanski <sebastien.szymanski@armadeus.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>