x86: export the symbol empty_zero_page on the 32-bit x86 architecture

The latest KVM driver wants to use the empty_zero_page symbol, and it's
not exported in 32-bit x86 (although it is exported by x86_64, s390, and
uml architectures).
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Cc: tglx@linutronix.de
Cc: linux-kernel@vger.kernel.com
Cc: kvm-devel@lists.sourceforge.net
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/kernel/i386_ksyms_32.c

@@ -2,6 +2,7 @@
 #include <asm/semaphore.h>
 #include <asm/checksum.h>
 #include <asm/desc.h>
+#include <asm/pgtable.h>
 
 EXPORT_SYMBOL(__down_failed);
 EXPORT_SYMBOL(__down_failed_interruptible);
@@ -29,3 +30,4 @@ EXPORT_SYMBOL(__read_lock_failed);
 #endif
 
 EXPORT_SYMBOL(csum_partial);
+EXPORT_SYMBOL(empty_zero_page);