dt-bindings: clock: st,stm32-rcc: support spread spectrum clocking

The addition of DT bindings for enabling and tuning spread spectrum
clocking generation is available only for the main PLL of stm32f{4,7}
platforms.

Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>

Link: https://lore.kernel.org/r/20250114182021.670435-3-dario.binacchi@amarulasolutions.com


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