Bug 2210288

Description of problem:
PXE booting on PPC fails, drops to grub prompt

Version-Release number of selected component (if applicable):
Starting from grub2-2.06-54.el9 until the present (2.06-61.el9)

How reproducible:
always

Steps to Reproduce:
1. Set up PXE server on ppc
2. Try to boot client
already described in these bugs: 
https://bugzilla.redhat.com/show_bug.cgi?id=2173015 (CentOS)
https://bugzilla.redhat.com/show_bug.cgi?id=2209435 (fedora)

Actual results:
# virsh start client --console
Domain 'client' started
Connected to domain 'client'
Escape character is ^] (Ctrl + ])
Populating /vdevice methods
Populating /vdevice/vty@30000000
Populating /vdevice/nvram@71000000
Populating /pci@800000020000000
                     00 0800 (D) : 1af4 1000    virtio [ net ]
                     00 1000 (D) : 1b36 000d    serial bus [ usb-xhci ]
                     00 1800 (D) : 1af4 1003    virtio [ serial ]
                     00 2000 (D) : 1af4 1002    legacy-device*
                     00 2800 (D) : 1af4 1005    legacy-device*
No NVRAM common partition, re-initializing...
Scanning USB 
  XHCI: Initializing
Using default console: /vdevice/vty@30000000
     
  Welcome to Open Firmware

  Copyright (c) 2004, 2017 IBM Corporation All rights reserved.
  This program and the accompanying materials are made available
  under the terms of the BSD License available at
  http://www.opensource.org/licenses/bsd-license.php


Trying to load:  from: /pci@800000020000000/ethernet@1 ... 
 Initializing NIC
  Reading MAC address from device: 52:54:00:de:8d:ab
  Requesting information via DHCP: done
  Using IPv4 address: 192.168.124.101
  Requesting file "/boot/grub2/powerpc-ieee1275/core.elf" via TFTP from 192.168.124.2
  Receiving data:  321 KBytes
  TFTP: Received /boot/grub2/powerpc-ieee1275/core.elf (321 KBytes)
  Successfully loaded
Welcome to GRUB!

error: ../../grub-core/script/function.c:119:can't find command `source'.



                               GRUB version 2.06

   Minimal BASH-like line editing is supported. For the first word, TAB   
   lists possible command completions. Anywhere else TAB lists possible   
   device or file completions.                                            


grub>

Expected results:
system boots

Additional info:
If default grub.cfg file in /var/lib/tftpboot/boot/grub2/powerpc-ieee1275/ (which is a one-liner: source boot/grub2/grub.cfg) is replaced by the actual grub.cfg file, then grub menu is loaded and failure looks like this:

  Booting `install RHEL-9.2'

error: ../../grub-core/script/function.c:119:can't find command `linux'.
error: ../../grub-core/script/function.c:119:can't find command `initrd'.

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