soc/tegra: pmc: Enable PMIC wake event on Tegra186

The PMIC wake event can be used to bring the system out of suspend based
on certain events happening on the PMIC (such as an RTC alarm).

Signed-off-by: Thierry Reding <treding@nvidia.com>
Acked-by: Jon Hunter <jonathanh@nvidia.com>
Tested-by: Jon Hunter <jonathanh@nvidia.com>