Mainline U-Boot with SPI, NVMe and SATA boot support

[sigmaris]

...
unrecognized JEDEC id bytes: ff, ff, ff
...

I normally only see this message if disabling SPI flash by bridging pins 23 (SPI CLK) and 25 (GND) on the Pi-2 Bus header. Basically it means the SPI flash chip isn't responding as expected on the SPI bus and can't be identified.

Check you're not disabling communication with the SPI flash somehow (e.g. grounding SPI CLK), if that's not the issue then I'd wonder if your SPI flash chip has a problem.