soc/tegra: pmc: Pass struct tegra_pmc * where possible

Instead of using the global pmc variable, pass around a pointer where
possible. Also, replace most occurrences of pr_*() functions by their
equivalent dev_*() functions, reusing the pmc->dev pointer.

It's not possible to get completely rid of the global variable because
some of the public API that this driver exposes still relies on it.
Signed-off-by: NThierry Reding <treding@nvidia.com>
Acked-by: NJon Hunter <jonathanh@nvidia.com>