PowerPC mac99 doesn't seem load -prom-env options

[giovariot]

Describe the issue
I've managed to install Yellow Dog Linux 2.3 following these intructions: https://eaasi.gitlab.io/program_docs/qemu-qed/recipes/yellowdoglinux/#installation.
Now my problem is that the openbios doesn't seem to load -prom-env set variables as it defaults to looking for a bootloader on the cdrom.

Here are the 2 -prom-env options I've set:
-prom-env "boot-device=hd:,\yaboot"
-prom-env "boot-args=conf=hd:,\yaboot.conf"

Therefore I'm not able to boot the OS through the yaboot powerpc bootloader.

Configuration

• UTM Version: 4.5.3 (99)
• macOS Version: 14.5 (23F79)
• Mac Chip (Intel, M1, ...): M1

Debug log
The Export Log... button stays greyed-out.

Upload VM
config.plist.zip

[osy]

bootindex seem to override -prom-env "boot-device=hd:,\yaboot". We should provide a way to disable bootindex.