@pholden
I've seen the same error when I was playing with LS1046AFRWY.
Look at this line:
[ 3.092365] Please append a correct "root=" boot option; here are the available partitions:
It seems that you didn't specify the `root=` option in u-boot env variable `bootargs`.
In my case it was
bootargs "root=/dev/ram0 rw console=ttyS0,115200 earlycon=uart8250,mmio,0x21c0500 ramdisk_size=0x10000000"
but then I forgot to upload the ramdisk via TFTP, and run "boot" command.
The same kernel panic is possible when you point wrong partition number of mmc in "root=" option.