Comment 4 for bug 1846397

After some debugging this seems to be u-boot caused change. By wiring uart directly without 96boards mezzanine I was able to test boot sequence with disconnected RX and TX.
And I can now see u-boot stopping at:
DRAM: 986 MiB
MMC: sdhci@07824000: 0, sdhci@07864000: 1
Loading Environment from FAT... OK
In: serial@78b0000
Out: serial@78b0000
Err: serial@78b0000
## Error: Can't overwrite "serial#"
## Error inserting "serial#" variable, errno=1
Net: Net Initialization Skipped
No ethernet found.
Hit any key to stop autoboot: 0
dragonboard410c =>

I will see if this is bug in v2019.04 or we need extra config flag...... stay tuned