Other Parts Discussed in Thread: AM62L
Tool/software:
Test on AM62L EVM board, boot from SD card which flashed with default .wic file to UBOOT console, flash eMMC follow the user guide:
=> mmc dev 0 1
switch to partitions #1, OK
mmc0(part 1) is current device
=> fatload mmc 1 ${loadaddr} tiboot3.bin
226016 bytes read in 11 ms (19.6 MiB/s)
=> mmc write ${loadaddr} 0x0 0x400
MMC write: dev # 0, block # 0, count 1024 ... 1024 blocks written: OK
=>
=>
=> fatload mmc 1 ${loadaddr} tispl.bin
762365 bytes read in 33 ms (22 MiB/s)
=> mmc write ${loadaddr} 0x400 0x1000
MMC write: dev # 0, block # 1024, count 4096 ... 4096 blocks written: OK
=> fatload mmc 1 ${loadaddr} u-boot.img
1181035 bytes read in 51 ms (22.1 MiB/s)
=> mmc write ${loadaddr} 0x1400 0x2000
MMC write: dev # 0, block # 5120, count 8192 ... 8192 blocks written: OK
=>
=> mmc partconf 0 1 1 1
=> mmc bootbus 0 2 0 0
Set to BOOT_BUS_WIDTH = 0x2, RESET = 0x0, BOOT_MODE = 0x0
=> mmc rst-function 0 1
=>
Switch to eMMC boot mode and power up again, no output from console.

I found it should be:
=> mmc partconf 0 1 2 1 => mmc bootbus 0 2 0 0