tegra: fdt: Add clock bindings

tegra: fdt: Add clock bindings

This adds a basic binding for the oscillator and peripheral clocks. The
second cell is the clock number, defined as the bit number within the clock
enable register if the peripheral clock.

This uses the RFC clock bindings from Grant Likely so may change later:

https://lkml.org/lkml/2011/12/12/498

It is taken from Stephen Warren's patch here:

http://patchwork.ozlabs.org/patch/141359/

Signed-off-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Tom Warren <twarren@nvidia.com>