soc/tegra: pmc: Remove non-existing L2 partition for Tegra124

Tegra124 does not have an L2 power partition and the L2 cache is part of
the cluster 0 non-CPU (CONC) partition. Remove the L2 as a valid
partition for Tegra124. The TRM also shows that there is no L2 partition
for Tegra124.

Signed-off-by: Jon Hunter <jonathanh@nvidia.com>
Reviewed-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: Thierry Reding <treding@nvidia.com>