ARM: tegra: pmc: convert PMC driver to support DT only

The Tegra kernel only support boot from DT now. Clean up the PMC driver
to support DT only, that includes:

* remove the ifdef of CONFIG_OF
* replace the static mapping of PMC addr to map from DT

Signed-off-by: Joseph Lo <josephl@nvidia.com>
Signed-off-by: Stephen Warren <swarren@nvidia.com>