sparc: Export symbols 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>
Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>