iomap: move the main iteration code into a separate file

Move the main iteration code into a separate file so that we can group
related functions in a single file instead of having a single enormous
source file.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>

fs/Makefile

@@ -52,7 +52,6 @@ obj-$(CONFIG_COREDUMP)		+= coredump.o
 obj-$(CONFIG_SYSCTL)		+= drop_caches.o
 
 obj-$(CONFIG_FHANDLE)		+= fhandle.o
-obj-$(CONFIG_FS_IOMAP)		+= iomap.o
 obj-y				+= iomap/
 
 obj-y				+= quota/

fs/iomap/Makefile

@@ -6,6 +6,7 @@
 obj-$(CONFIG_FS_IOMAP)		+= iomap.o
 
 iomap-y				+= \
+					apply.o \
 					buffered-io.o \
 					direct-io.o \
 					fiemap.o \

fs/iomap/apply.c

@@ -7,23 +7,8 @@
 #include <linux/compiler.h>
 #include <linux/fs.h>
 #include <linux/iomap.h>
-#include <linux/uaccess.h>
-#include <linux/gfp.h>
-#include <linux/migrate.h>
-#include <linux/mm.h>
-#include <linux/mm_inline.h>
-#include <linux/swap.h>
-#include <linux/pagemap.h>
-#include <linux/pagevec.h>
-#include <linux/file.h>
-#include <linux/uio.h>
-#include <linux/backing-dev.h>
-#include <linux/buffer_head.h>
-#include <linux/task_io_accounting_ops.h>
-#include <linux/dax.h>
-#include <linux/sched/signal.h>
 
-#include "internal.h"
+#include "../internal.h"
 
 /*
  * Execute a iomap write on a segment of the mapping that spans a