dt-bindings: clock: Replace common binding with link to schema

dt-bindings: clock: Replace common binding with link to schema

The contents of the clock binding have been moved to the clock binding
schema in the dtschema repository. The desire is for common bindings to
be hosted in the dtschema repository.

Replace the contents with a link to the clock binding schema as there
are still many references to clock-bindings.txt in the tree. This will
prevent additions without a schema.

Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220428154154.2284317-1-robh@kernel.org
Signed-off-by: Stephen Boyd <sboyd@kernel.org>