refine code comments: clarify misleading names and comments for `thre…

…ad_rpc_alloc_*_payload` APIs

The `thread_rpc_alloc_*_payload` APIs are consistent with the `thread_shm_type` enumerations, as seen in the `alloc_shm` function. However, the name and comments of `thread_rpc_alloc_payload` might be misleading, suggesting it is a universal API. To maintain backward compatibility, only the code comments have been updated for clarity.

core/include/kernel/thread.h

@@ -244,7 +244,8 @@ bool thread_is_in_normal_mode(void);
 bool thread_is_from_abort_mode(void);
 
 /**
- * Allocates data for payload buffers.
+ * Allocates data for payload buffers only shared with user space applications. 
+ * Ensure consistency with the enumeration `THREAD_SHM_TYPE_APPLICATION`.
  *
  * @size:	size in bytes of payload buffer
  *
@@ -260,7 +261,8 @@ struct mobj *thread_rpc_alloc_payload(size_t size);
 void thread_rpc_free_payload(struct mobj *mobj);
 
 /**
- * Allocate data for payload buffers only shared with the non-secure kernel
+ * Allocate data for payload buffers only shared with the non-secure kernel. 
+ * Ensure consistency with the enumeration `THREAD_SHM_TYPE_KERNEL_PRIVATE`.
  *
  * @size:	size in bytes of payload buffer
  *
@@ -333,8 +335,8 @@ uint32_t thread_rpc_cmd(uint32_t cmd, size_t num_params,
 		struct thread_param *params);
 
 /**
- * Allocate data for payload buffers.
- * Buffer is exported to user mode applications.
+ * Allocate data for payload buffers shared with both user space applications the non-secure kernel. 
+ * Ensure consistency with the enumeration `THREAD_SHM_TYPE_GLOBAL`.
  *
  * @size:	size in bytes of payload buffer
  *