arm64: tegra: Add PMU node for Tegra194

Populate the device-tree node for the PMU device on Tegra194. This also
fixes the following warning that is observed on booting Tegra194.

 ERR KERN kvm: pmu event creation failed -2

Signed-off-by: Jon Hunter <jonathanh@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>