ARM: tegra: Add dvfs rails

ARM: tegra: Add dvfs rails

The previous version of dvfs handled requirements between two
different voltage rails by using two sets of dvfs tables, one
for each rail.  That method fails for vdd_aon, which must be
within 170 mV of vdd_core.

Instead, have each dvfs clock only set the voltage rail that
it directly depends on, and add a relationship system to the
voltage rails.  When the voltage changes on one rail, it calls
update on all the rails that depend on it.  The dependent rails
compare the new voltage of the original rail to their own
voltage, and update their own voltage as necessary.

Change-Id: I17b30a61c7c0c01e44702ab486238789abd47330
Signed-off-by: Colin Cross <ccross@android.com>