ARM: dts: stm32mp1: DT alignment with Linux 5.6-rc1

ARM: dts: stm32mp1: DT alignment with Linux 5.6-rc1

This commit manages diversity for STM32M15x SOCs with:
- 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.
- new files to manage security diversity on STM32MP15x SOCs.
  On STM32MP15xY, "Y" gives information:
  -Y = A means no cryp IP and no secure boot.
  -Y = C means cryp IP + secure boot.
- stm32mp157 pinctrl files to better manage package diversity.

Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
Acked-by: Patrice Chotard <patrice.chotard@st.com>