Multiple Tegra drivers need to retrieve Memory Controller and there is
duplication of the retrieval code among the drivers.

Add new devm_tegra_memory_controller_get() helper to remove the code's
duplication and to fix put_device() which was missed in the duplicated
code. Make EMC drivers to use the new helper.
Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Acked-by: Thierry Reding <treding@nvidia.com>
Link: https://lore.kernel.org/r/20201104164923.21238-29-digetx@gmail.comSigned-off-by: Krzysztof Kozlowski <krzk@kernel.org>