soc/tegra: pmc: Pass PMC to tegra_powergate_power_up()

tegra_powergate_sequence_power_up() makes up a struct tegra_powergate
from scratch in order to reuse the same code as used by the generic PM
domain implementation. However, subsequent patches will need to access
the struct tegra_pmc * embedded in the powergate structure, so we need
to make sure we always pass it in.

Tested-by: Hector Martin <marcan@marcan.st>
Tested-by: Andre Heider <a.heider@gmail.com>
Tested-by: Mikko Perttunen <mperttunen@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>