kfifo: don't include dma-mapping.h in kfifo.h

Nothing in kfifo.h directly needs dma-mapping.h, only two macros
use DMA_MAPPING_ERROR when actually instantiated.  Drop the
dma-mapping.h include to reduce include bloat.

Add an explicity <linux/io.h> include to drivers/mailbox/omap-mailbox.c
as that file uses __raw_readl and __raw_writel through a complicated
include chain involving <linux/dma-mapping.h>

Fixes: d52b761e4b ("kfifo: add kfifo_dma_out_prepare_mapped()")
Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20241023055317.313234-1-hch@lst.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/mailbox/omap-mailbox.c

@@ -15,6 +15,7 @@
 #include <linux/slab.h>
 #include <linux/kfifo.h>
 #include <linux/err.h>
+#include <linux/io.h>
 #include <linux/module.h>
 #include <linux/of.h>
 #include <linux/platform_device.h>

include/linux/kfifo.h

@@ -37,7 +37,6 @@
  */
 
 #include <linux/array_size.h>
-#include <linux/dma-mapping.h>
 #include <linux/spinlock.h>
 #include <linux/stddef.h>
 #include <linux/types.h>

samples/kfifo/dma-example.c

@@ -9,6 +9,7 @@
 #include <linux/kfifo.h>
 #include <linux/module.h>
 #include <linux/scatterlist.h>
+#include <linux/dma-mapping.h>
 
 /*
  * This module shows how to handle fifo dma operations.