Integrate u-boot-seco-imx/seco_lf_v2021.04_develop_962_ym
[962][ENV_CONF][MX6_DTBO] add overlay definition and update them in env_conf.h
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[926] fix seco constants names and typos
- SECO_DEV becomes SECO_DEV_TYPE
- EXT_SD becomes SD_EXT
- FILE becomes FILENAME
- add ENV_DEFAULT_FDT_FILE
- use correct id for external sd instead of "0"
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[962] fix bus_id for External SD print_boot_device() (board/seco/common/board_imx6.c) uses information contained in the CPU registers to identify the current boot device. The boot device is identified among the ones specified into boot_mem_dev_list; since commit f7da4b01, the function check if the bus id of the current boot device is equal to the one in boot_mem_dev_list; if this control fails, the boot device is skipped; if no boot device is identified, the boot device is considerd "Unknow". In order to corretly detect the boot device for 962 board we have to correctly specify the bus id.