feat(stm32mp1-fdts): add DT files for STM32MP13

STM32MP13 is a single Cortex-A7 CPU, without co-processor.
As for STM32MP15x SoC family, STM32MP15x SoCs come with different
features, depending on SoC version. Each peripheral node is created.
Some are left empty for the moment , and will be filled later on.

Change-Id: I0166bb70dfa7f717e89e89883b059a5b873c4ef7
Signed-off-by: Yann Gautier <yann.gautier@st.com>