proc: introduce proc_create_single{,_data}

Variants of proc_create{,_data} that directly take a seq_file show
callback and drastically reduces the boilerplate code in the callers.

All trivial callers converted over.

Signed-off-by: Christoph Hellwig <hch@lst.de>
diff --git a/arch/arm/kernel/dma.c b/arch/arm/kernel/dma.c
index e651c4d..6739d37 100644
--- a/arch/arm/kernel/dma.c
+++ b/arch/arm/kernel/dma.c
@@ -276,21 +276,9 @@
 	return 0;
 }
 
-static int proc_dma_open(struct inode *inode, struct file *file)
-{
-	return single_open(file, proc_dma_show, NULL);
-}
-
-static const struct file_operations proc_dma_operations = {
-	.open		= proc_dma_open,
-	.read		= seq_read,
-	.llseek		= seq_lseek,
-	.release	= single_release,
-};
-
 static int __init proc_dma_init(void)
 {
-	proc_create("dma", 0, NULL, &proc_dma_operations);
+	proc_create_single("dma", 0, NULL, proc_dma_show);
 	return 0;
 }