mm: filemap: Fix microblaze build failure with 'mmu_defconfig'

Commit f9ce0be71d ("mm: Cleanup faultaround and finish_fault()
codepaths") added a call to 'update_mmu_cache()' in mm/filemap.c, which
breaks the build for microblaze:

  | mm/filemap.c: In function 'filemap_map_pages':
  | mm/filemap.c:3153:3: error: implicit declaration of function 'update_mmu_cache'; did you mean 'update_mmu_tlb'?

Include asm/tlbflush.h in mm/filemap.c to make sure that the function
(or indeed, macro) is available.

Reported-by: Guenter Roeck <linux@roeck-us.net>
Tested-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20210209202449.GA104837@roeck-us.net
Signed-off-by: Will Deacon <will@kernel.org>

mm/filemap.c

@@ -43,6 +43,7 @@
 #include <linux/ramfs.h>
 #include <linux/page_idle.h>
 #include <asm/pgalloc.h>
+#include <asm/tlbflush.h>
 #include "internal.h"
 
 #define CREATE_TRACE_POINTS