dt-bindings: rcc: stm32: select the "secure" path for stm32mp13

Like for stm32mp15, when stm32 RCC node is used to interact with a secure
context (using clock SCMI protocol), a different path has to be used for
yaml verification.

Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>
Acked-by: Rob Herring <robh@kernel.org>