btrfs: add helper folio_end()

There are several cases of folio_pos + folio_size, add a convenience
helper for that. This is a local helper and not proposed as folio API
because it does not seem to be heavily used elsewhere:

A quick grep (folio_size + folio_end) in fs/ shows

     24 btrfs
      4 iomap
      4 ext4
      2 xfs
      2 netfs
      1 gfs2
      1 f2fs
      1 bcachefs
      1 buffer.c

Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/misc.h

@@ -7,6 +7,8 @@
 #include <linux/bitmap.h>
 #include <linux/sched.h>
 #include <linux/wait.h>
+#include <linux/mm.h>
+#include <linux/pagemap.h>
 #include <linux/math64.h>
 #include <linux/rbtree.h>
 
@@ -158,4 +160,9 @@ static inline bool bitmap_test_range_all_zero(const unsigned long *addr,
 	return (found_set == start + nbits);
 }
 
+static inline u64 folio_end(struct folio *folio)
+{
+	return folio_pos(folio) + folio_size(folio);
+}
+
 #endif