ARM: tegra: Add the DFLL to Tegra124 device tree

The DFLL clocksource is a separate IP block from the usual
clock-and-reset controller, so it gets its own device tree node.

Signed-off-by: Tuomas Tynkkynen <ttynkkynen@nvidia.com>
Signed-off-by: Mikko Perttunen <mikko.perttunen@kapsi.fi>
Acked-by: Michael Turquette <mturquette@linaro.org>
Signed-off-by: Thierry Reding <treding@nvidia.com>