soc/tegra: pmc: Add Tegra194 compatibility string

The Tegra194 PMC is mostly compatible with Tegra186, including in all
currently supported features. As such, add a new compatibility string
but point to the existing Tegra186 SoC data for now.

Signed-off-by: Mikko Perttunen <mperttunen@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>