dt-bindings: ti: dpll: add spread spectrum support

DT bindings for enabling and adjusting spread spectrum clocking have
been added.

Signed-off-by: Dario Binacchi <dariobin@libero.it>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20210606202253.31649-3-dariobin@libero.it


Signed-off-by: Stephen Boyd <sboyd@kernel.org>