hw/ppc: Enable fadump for PSeries

hw/ppc: Enable fadump for PSeries

With all support in place for preserving memory regions, enable fadump by
exporting the "ibm,kernel-dump" property in the device tree, representing
the fadump dump information, in case of a crash.

Currently "ibm,configure-kernel-dump" RTAS call is already registered,
which tells the kernel that the platform (QEMU) supports fadump.

Now, in case of a crash, if fadump was registered, we also pass
"ibm,kernel-dump" in device tree, which tells the kernel that the fadump
dump is active.

Pass "fadump=on" to enable Linux to use firmware assisted dump.

Logs of a linux boot with firmware assisted dump:

    $ ./build/qemu-system-ppc64 -M pseries,x-vof=on --cpu power10 --smp 4 -m 4G -kernel some-vmlinux -initrd some-initrd -append "debug fadump=on crashkernel=1G" -nographic

    [    0.000000] fadump: Reserved 1024MB of memory at 0x00000040000000 (System RAM: 4096MB)
    [    0.000000] fadump: Initialized 0x40000000 bytes cma area at 1024MB from 0x400102a8 bytes of memory reserved for firmware-assisted dump
    ...
    [    1.084686] rtas fadump: Registration is successful!
    ...
    # cat /sys/kernel/debug/powerpc/fadump_region
    CPU :[0x00000040000000-0x000000400013df] 0x13e0 bytes, Dumped: 0x0
    HPTE:[0x000000400013e0-0x000000400013df] 0x0 bytes, Dumped: 0x0
    DUMP: Src: 0x00000000000000, Dest: 0x00000040010000, Size: 0x40000000, Dumped: 0x0 bytes

    [0x0000000921a000-0x0000000921a7ff]: cmdline append: ''
    # echo c > /proc/sysrq-trigger

The fadump boot after crash:

    [    0.000000] rtas fadump: Firmware-assisted dump is active.
    [    0.000000] fadump: Updated cmdline: debug fadump=on crashkernel=1G
    [    0.000000] fadump: Firmware-assisted dump is active.
    [    0.000000] fadump: Reserving 3072MB of memory at 0x00000040000000 for preserving crash data
    ....
    # file /proc/vmcore
    /proc/vmcore: ELF 64-bit LSB core file, 64-bit PowerPC or cisco 7500, OpenPOWER ELF V2 ABI, version 1 (SYSV), SVR4-style

Analysing the vmcore with crash-utility:

          KERNEL: vmlinux-6.14-rc2
        DUMPFILE: vmcore-fc92fb373aa0
            CPUS: 4
            DATE: Wed Mar 12 23:39:23 CDT 2025
          UPTIME: 00:00:22
    LOAD AVERAGE: 0.13, 0.03, 0.01
           TASKS: 95
        NODENAME: buildroot
         RELEASE: 6.12.0-rc4+
         VERSION: #1 SMP Fri Jan  3 00:15:17 IST 2025
         MACHINE: ppc64le  (1000 Mhz)
          MEMORY: 4 GB
           PANIC: "Kernel panic - not syncing: sysrq triggered crash"
             PID: 269
         COMMAND: "sh"
            TASK: c00000000a050b00  [THREAD_INFO: c00000000a050b00]
             CPU: 0
           STATE: TASK_RUNNING (PANIC)

Signed-off-by: Aditya Gupta <adityag@linux.ibm.com>
Reviewed-by: Sourabh Jain <sourabhjain@linux.ibm.com>
Tested-by: Shivang Upadhyay <shivangu@linux.ibm.com>
Link: https://lore.kernel.org/qemu-devel/20251021134823.1861675-7-adityag@linux.ibm.com
Signed-off-by: Harsh Prateek Bora <harshpb@linux.ibm.com>