clk: tegra: Add EMC clock driver

The driver is currently only tested on Tegra124 Jetson TK1, but should
work with other Tegra124 boards, provided that correct EMC tables are
provided through the device tree. Older chip models have differing
timing change sequences, so they are not currently supported.

Signed-off-by: Mikko Perttunen <mperttunen@nvidia.com>
Signed-off-by: Tomeu Vizoso <tomeu.vizoso@collabora.com>
[treding@nvidia.com: use more consistent function names]
Signed-off-by: Thierry Reding <treding@nvidia.com>