STM32MP151 and STM32MP153 were not explicitly supported through
stm32mp157c.dts. This commit adds dedicated files to support all STM32MP15
SOCs family.

The differences between those SOCs are:
 -STM32MP151 [1]: common file.
 -STM32MP153 [2]: STM32MP151 + CANs + a second CortexA7-CPU.
 -STM32MP157 [3]: STM32MP153 + DSI + GPU.

[1] https://www.st.com/resource/en/reference_manual/dm00366349.pdf
[2] https://www.st.com/resource/en/reference_manual/dm00366355.pdf
[3] https://www.st.com/resource/en/reference_manual/dm00327659.pdfSigned-off-by: Alexandre Torgue <alexandre.torgue@st.com>