ANDROID: export symbols needed by Rust Binder

To call these functions from a vendor module, it is necessary to export
them.

The functions file_close_fd and task_work_add are needed to reimplement
binder's `binder_deferred_fd_close` function.

The `zap_page_range_single` function is needed to free pages when
Binder's shrinker runs.

Bug: 388786466
Change-Id: If05030b5a4c0180ff839b6f86ab0b86b87703f2b
Signed-off-by: Alice Ryhl <aliceryhl@google.com>

fs/file.c

@@ -793,6 +793,7 @@ struct file *file_close_fd(unsigned int fd)
 
 	return file;
 }
+EXPORT_SYMBOL_GPL(file_close_fd);
 
 void do_close_on_exec(struct files_struct *files)
 {

kernel/task_work.c

@@ -108,6 +108,7 @@ int task_work_add(struct task_struct *task, struct callback_head *work,
 
 	return 0;
 }
+EXPORT_SYMBOL_GPL(task_work_add);
 
 /**
  * task_work_cancel_match - cancel a pending work added by task_work_add()

mm/memory.c

@@ -1940,6 +1940,7 @@ void zap_page_range_single(struct vm_area_struct *vma, unsigned long address,
 	tlb_finish_mmu(&tlb);
 	hugetlb_zap_end(vma, details);
 }
+EXPORT_SYMBOL_GPL(zap_page_range_single);
 
 /**
  * zap_vma_ptes - remove ptes mapping the vma