I think the Bios changed position. It is now in home\pi\retropie\bios\amiga and it must contain
Kickstart v1.3 rev 34.5 (1987)(Commodore)(A500-A1000-A2000-CDTV).rom
Kickstart v2.05 rev 37.350 (1992)(Commodore)(A600HD).rom
Kickstart v3.1 rev 40.68 (1993)(Commodore)(A1200).rom
I am not sure about the 600 rom if it is necessary though.