Update spawn doc for xpu (#33497)

* update spawn doc for xpu, test=ducument_fix

* add note for gpu and xpu, test=document_fix

python/paddle/distributed/spawn.py

@@ -335,7 +335,9 @@ def spawn(func, args=(), nprocs=-1, join=True, daemon=False, **options):
     Start multiple processes with ``spawn`` method for parallel training.
 
     .. note::
-        ``spawn`` now only supports GPU collective mode.
+        ``spawn`` now only supports GPU or XPU collective mode. The collective mode
+        of GPU and XPU cannot be started at the same time, so the option `gpus` and
+        `xpus` cannot be configured at the same time.
 
     Args:
         func (function): The target function is called by spawned process.
@@ -346,11 +348,8 @@ def spawn(func, args=(), nprocs=-1, join=True, daemon=False, **options):
             when nprocs is -1, the available device will be obtained from
             the environment variable when the model is executed: If use GPU,
             the currently available device ID is obtained from the environment
-            variable CUDA_VISIBLE_DEVICES; If use CPU, the currently available
-            CPU number is obtained from the environment variable CPU_NUM. 
-            For example, export CPU_NUM=4, if the environment variable is not set, 
-            the spawn method will add default value to the environment variable 
-            and set its value to 1.
+            variable CUDA_VISIBLE_DEVICES; If use XPU, the currently available
+            device ID is obtained from the environment variable XPU_VISIBLE_DEVICES.
         join (bool, optional): Perform a blocking join on all spawned processes.
             Default: True.
         daemon (bool, optional): The spawned processes' daemon flag. Default: False.
@@ -363,7 +362,9 @@ def spawn(func, args=(), nprocs=-1, join=True, daemon=False, **options):
             or ``forkserver`` method. Default: "spawn" ;
             (2) gpus (string): The training process will run on the
             selected gpus, such as "0,1,2,3". Default: None;
-            (3) ips (string): Paddle cluster nodes ips, such as 
+            (3) xpus (string): The training process will run on the
+            selected xpus, such as "0,1,2,3". Default: None;
+            (4) ips (string): Paddle cluster nodes ips, such as
             "192.168.0.16,192.168.0.17". Default: "127.0.0.1" .
 
     Returns: