scripts/gdb: make get_thread_info accept pointers

get_thread_info ($lx_thread_info) only accepted a dereferenced task
parameter.  Passing a pointer to a task_struct (like $lx_per_cpu does with
KGDB) threw an exception.

With this patch, both (dereferenced values and pointers) are accepted.

Before (on x86, KGDB):
>>> p $lx_per_cpu(cpu_info)
Traceback (most recent call last):
  File "./scripts/gdb/linux/cpus.py", line 158, in invoke
    return per_cpu(var_ptr, cpu)
           ^^^^^^^^^^^^^^^^^^^^^
  File "./scripts/gdb/linux/cpus.py", line 42, in per_cpu
    cpu = get_current_cpu()
          ^^^^^^^^^^^^^^^^^
  File "./scripts/gdb/linux/cpus.py", line 33, in get_current_cpu
    return tasks.get_thread_info(tasks.get_task_by_pid(tid))['cpu']
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "./scripts/gdb/linux/tasks.py", line 88, in get_thread_info
    if task.type.fields()[0].type == thread_info_type.get_type():
       ~~~~~~~~~~~~~~~~~~^^^
IndexError: list index out of range

Link: https://lkml.kernel.org/r/20240425153501.749966-4-mail@florommel.de
Signed-off-by: Florian Rommel <mail@florommel.de>
Cc: Andrew Jones <ajones@ventanamicro.com>
Cc: Deepak Gupta <debug@rivosinc.com>
Cc: Jan Kiszka <jan.kiszka@siemens.com>
Cc: Kieran Bingham <kbingham@kernel.org>
Cc: Kuan-Ying Lee <Kuan-Ying.Lee@mediatek.com>
Cc: Palmer Dabbelt <palmer@rivosinc.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

scripts/gdb/linux/tasks.py

@@ -85,7 +85,7 @@ thread_info_type = utils.CachedType("struct thread_info")
 
 def get_thread_info(task):
     thread_info_ptr_type = thread_info_type.get_type().pointer()
-    if task.type.fields()[0].type == thread_info_type.get_type():
+    if task_type.get_type().fields()[0].type == thread_info_type.get_type():
         return task['thread_info']
     thread_info = task['stack'].cast(thread_info_ptr_type)
     return thread_info.dereference()