ARM: tegra: Overhaul Venice2 regulators

Some of the regulators and the relationships to other regulators are
wrong. This commit attempts to rectify this by making them more similar
to what the schematics contain. This starts by adding a +VDD_MUX supply
that represents the 12V input and derives the main +3.3V_SYS and +5V_SYS
supplies from that. The majority of the other regulators derive from one
of those three.

While at it, rename the regulators to match the names in the schematics
to make them easier to match up.

Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Stephen Warren <swarren@nvidia.com>