FINALLY FOUND IT!
I found another server R520 with 051XDX Motherboard (exactly same as mine) and extracted the SPI Flash ROM from chip… (Chip is Adesto AT25DF321A-SH-T)
The rom is 100% working…
You can find all ROMs that I have here…
Mega Folder (IDRAC SPI ROMs)
Credits to people found other IDRAC ROMs:
https://winraid.level1techs.com/t/problem-dell-r720xd-idrac-bios-recovery/32658