tegra: Rename NV_PA_PMC_BASE to TEGRA2_PMC_BASE

Change this name to fit with the current convention in the Tegra
header file.

Signed-off-by: Simon Glass <sjg@chromium.org>
Acked-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Tom Warren <twarren@nvidia.com>