dt-bindings: clock: New bindings for TI Davinci PSC

This adds a new binding for the Power Sleep Controller (PSC) for the
mach-davinci family of processors.

Note: Although TI Keystone has a very similar PSC, we are not using the
existing bindings. Keystone is using a legacy one-node-per-clock binding
(actually two nodes if you count the separate reset binding for the same
IP block). Also, some davinci LPSCs have quirks that aren't handled by
the keystone bindings, so we would be adding one compatible string per
clock with quirks instead of just a new compatible string for each
controller.

Signed-off-by: David Lechner <david@lechnology.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>