mm/zsmalloc: make zsmalloc module-buildable

Now, we can build zsmalloc as module because unmap_kernel_range was
exported.
Signed-off-by: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Jerome Marchand <jmarchan@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/Kconfig

@@ -551,7 +551,7 @@ config MEM_SOFT_DIRTY
 	  See Documentation/vm/soft-dirty.txt for more details.
 
 config ZSMALLOC
-	bool "Memory allocator for compressed pages"
+	tristate "Memory allocator for compressed pages"
 	depends on MMU
 	default n
 	help