Revert "mm/hmm: fix header file if/else/endif maze"

This reverts commit 25df8b83e867dcfb660123e9589ebf6f094fcdd3 which is
commit b28b08de upstream.

There are still build errors with this patch applied, and the upstream
patches do not seem to apply anymore, so reverting this patch seems like
the best thing to do at this point in time.
Reported-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Михаил Носов <drdeimosnn@gmail.com>
Cc: Jérôme Glisse <jglisse@redhat.com>
Cc: Balbir Singh <bsingharora@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Evgeny Baskakov <ebaskakov@nvidia.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

include/linux/hmm.h

@@ -498,16 +498,23 @@ struct hmm_device {
 struct hmm_device *hmm_device_new(void *drvdata);
 void hmm_device_put(struct hmm_device *hmm_device);
 #endif /* CONFIG_DEVICE_PRIVATE || CONFIG_DEVICE_PUBLIC */
+#endif /* IS_ENABLED(CONFIG_HMM) */
 
 /* Below are for HMM internal use only! Not to be used by device driver! */
+#if IS_ENABLED(CONFIG_HMM_MIRROR)
 void hmm_mm_destroy(struct mm_struct *mm);
 
 static inline void hmm_mm_init(struct mm_struct *mm)
 {
 	mm->hmm = NULL;
 }
+#else /* IS_ENABLED(CONFIG_HMM_MIRROR) */
+static inline void hmm_mm_destroy(struct mm_struct *mm) {}
+static inline void hmm_mm_init(struct mm_struct *mm) {}
+#endif /* IS_ENABLED(CONFIG_HMM_MIRROR) */
+
+
 #else /* IS_ENABLED(CONFIG_HMM) */
 static inline void hmm_mm_destroy(struct mm_struct *mm) {}
 static inline void hmm_mm_init(struct mm_struct *mm) {}
-#endif /* IS_ENABLED(CONFIG_HMM) */
 #endif /* LINUX_HMM_H */