unicore32: turn flush_dcache_mmap_lock into a no-op

Unicore doesn't walk the VMA tree in its flush_dcache_page()
implementation, so has no need to take the tree_lock.

Link: http://lkml.kernel.org/r/20180313132639.17387-5-willy@infradead.org
Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
Cc: Darrick J. Wong <darrick.wong@oracle.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Jeff Layton <jlayton@kernel.org>
Cc: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/unicore32/include/asm/cacheflush.h

@@ -170,10 +170,8 @@ extern void flush_cache_page(struct vm_area_struct *vma,
 #define ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE 1
 extern void flush_dcache_page(struct page *);
 
-#define flush_dcache_mmap_lock(mapping)			\
-	spin_lock_irq(&(mapping)->tree_lock)
-#define flush_dcache_mmap_unlock(mapping)		\
-	spin_unlock_irq(&(mapping)->tree_lock)
+#define flush_dcache_mmap_lock(mapping)		do { } while (0)
+#define flush_dcache_mmap_unlock(mapping)	do { } while (0)
 
 #define flush_icache_user_range(vma, page, addr, len)	\
 	flush_dcache_page(page)