dt-bindings: cpufreq: tegra124: remove cpu_lp clock from required properties

dt-bindings: cpufreq: tegra124: remove cpu_lp clock from required properties

The cpu_lp clock property is only needed when the CPUfreq driver
supports CPU cluster switching. But it was not a design for this driver
and it didn't handle that as well. So removing this property.

Cc: devicetree@vger.kernel.org
Signed-off-by: Joseph Lo <josephl@nvidia.com>
Acked-by: Jon Hunter <jonathanh@nvidia.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Thierry Reding <treding@nvidia.com>