[OE-core] wic creates ext4 images that read really slow in u-boot

[Mike Looijmans]

Took me a while to figure out why my board took 90 seconds to boot suddenly.

The issue turned out to be the ext4 partition created by wic.

On a "wic" created ext4 disk, this is what u-boot does:

ZynqMP> load mmc 0:2 0x100000 /lib/firmware/fpga.bin
19311092 bytes read in 85529 ms (219.7 KiB/s)


Now if I boot the board rename and copy that file onto itself, then it's 
suddenly normal again when I reboot the board:

ZynqMP> load mmc 0:2 0x100000 /lib/firmware/fpga.bin
19311092 bytes read in 1426 ms (12.9 MiB/s)


I checked with other files, and it turns out that ANY big file written by wic 
will read very slow (at 200k/s) but if I make a copy from a running system, it 
suddenly reads fast.

I'm not knowledgeable on ext4, so any ideas what's being passed onto the image 
creation tool that causes this?