arm: Export empty_zero_page for ZERO_PAGE usage in modules.

ext4 uses ZERO_PAGE(0) to zero out blocks.  We need to export
different symbols in different arches for the usage of ZERO_PAGE
in modules.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c
index d41a75e..2d6d682 100644
--- a/arch/arm/mm/mmu.c
+++ b/arch/arm/mm/mmu.c
@@ -35,6 +35,7 @@
  * zero-initialized data and COW.
  */
 struct page *empty_zero_page;
+EXPORT_SYMBOL(empty_zero_page);
 
 /*
  * The pmd table for the upper-most set of pages.