I have now got Debian sid automatically booting from my m.2 SSD.
Note that this is a hacky solution because it uses the booti command to load the kernel and initrd instead of using the u-boot sysboot command to parse the extlinux.conf but its a step in the right direction and proof that direct SSD boot is possible with a current image and the current official u-boot/firmware, 2.11.5.
I did not need to modify the default fstab nor the extlinux.conf included with sid. The only modifaction to the standard sid image was to resize the root btrfs partition to fill the disk using gparted.
You might want to run env default -a -f to reset your current u-boot config before running the following u-boot commands:
setenv boot_targets nvme0
setenv preboot 'run chipa_set_uboot;pci enum;nvme scan'
setenv bootargs 'root=/dev/nvme0n1p4 console=tty1 console=ttyS0,115200 debug rootwait earlycon=sbi'
setenv kernel_comp_addr_r 0x50000000
setenv kernel_comp_size 0x04000000
setenv bootcmd 'fatload nvme 0:3 ${kernel_addr_r} vmlinuz-5.15.0-vf2-104+; fatload nvme 0:3 ${ramdisk_addr_r} initrd.img-5.15.0-vf2-104+; fatload nvme 0:3 ${fdt_addr_r} dtb-5.15.0-vf2-104+/starfive/jh7110-visionfive-v2.dtb; booti $kernel_addr_r $ramdisk_addr_r:$filesize $fdt_addr_r'
saveenv