pmdomain: tegra: Move Kconfig option to the pmdomain subsystem

The Kconfig option belongs closer to the corresponding implementation,
hence let's move it from the soc subsystem to the pmdomain subsystem.

Cc: Thierry Reding <thierry.reding@gmail.com>
Cc: Jonathan Hunter <jonathanh@nvidia.com>
Cc: Mikko Perttunen <mperttunen@nvidia.com>
Cc: <linux-tegra@vger.kernel.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>