dt-bindings: mfd: Document STM32 low power timer bindings

Add a subnode to STM low power timer bindings to support timer driver

Signed-off-by: Benjamin Gaignard <benjamin.gaignard@st.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
1 file changed