soc/tegra: bpmp: Implement generic PM domains

The BPMP firmware, found on Tegra186 and later, provides an ABI that can
be used to enable and disable power to several power partitions in Tegra
SoCs. The ABI allows for enumeration of the available power partitions,
so the driver can be reused on future generations, provided the BPMP ABI
remains stable.

Based on work by Stefan Kristiansson <stefank@nvidia.com> and Mikko
Perttunen <mperttunen@nvidia.com>.

Signed-off-by: Thierry Reding <treding@nvidia.com>
Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Thierry Reding <treding@nvidia.com>