mm: shrinkers: add missing includes for undeclared types

The shrinker.h header depends on a user including other headers before it
for types used by shrinker.h.  Fix this by including the appropriate
headers in shrinker.h.

./include/linux/shrinker.h:13:9: error: unknown type name `gfp_t'
   13 |         gfp_t gfp_mask;
      |         ^~~~~
./include/linux/shrinker.h:71:26: error: field `list' has incomplete type
   71 |         struct list_head list;
      |                          ^~~~
./include/linux/shrinker.h:82:9: error: unknown type name `atomic_long_t'
   82 |         atomic_long_t *nr_deferred;
      |

Link: https://lkml.kernel.org/r/20221114235949.201749-1-tjmercier@google.com
Fixes: 83aeeada ("vmscan: use atomic-long for shrinker batching")
Fixes: b0d40c92 ("superblock: introduce per-sb cache shrinker infrastructure")
Signed-off-by: T.J. Mercier <tjmercier@google.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Dave Chinner <dchinner@redhat.com>
Cc: Konstantin Khlebnikov <khlebnikov@openvz.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

include/linux/shrinker.h

@@ -2,6 +2,9 @@
 #ifndef _LINUX_SHRINKER_H
 #define _LINUX_SHRINKER_H
 
+#include <linux/atomic.h>
+#include <linux/types.h>
+
 /*
  * This struct is used to pass information from page reclaim to the shrinkers.
  * We consolidate the values for easier extension later.