ARM: dts: stm32: Adapt STM32MP157 DK boards to stm32 DT diversity

To handle STM32MP15 SOCs diversity, some updates have to been done.
This commit mainly adapt dk1 board to include the correct package and the
correct SOC version. A new file has been created to factorize common parts.

Signed-off-by: Alexandre Torgue <alexandre.torgue@st.com>