tegra2: Add more clock functions

tegra2: Add more clock functions

This adds most of the clock functions required by board and driver code:

-query and adjust peripheral clocks
-query and adjust PLLs
-reset and enable control

These functions are plumbed in as required.

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