clk: tegra: Add la clock for Tegra210

This clock is needed by the memory built-in self test work around.

Signed-off-by: Peter De Schrijver <pdeschrijver@nvidia.com>
Reviewed-by: Jon Hunter <jonathanh@nvidia.com>
Tested-by: Jon Hunter <jonathanh@nvidia.com>
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>