stm32mp1: add runtime information in environment

Set board name with the first dts compatible found in DT
code under CONFIG_ENV_VARS_UBOOT_RUNTIME_CONFIG

The result with DEVICE_TREE=stm32mp157c-ev1 is:
    STM32MP> env print
    	board=stm32mp1
    	board_name=stm32mp157c-ev1

Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
2 files changed