powerpc: Move agp_special_page export to where it is defined

... instead of exporting it in arch/*/kernel/ppc_ksyms.c.

Signed-off-by: Paul Mackerras <paulus@samba.org>
diff --git a/arch/ppc/mm/init.c b/arch/ppc/mm/init.c
index 5e9ef23..db94efd 100644
--- a/arch/ppc/mm/init.c
+++ b/arch/ppc/mm/init.c
@@ -69,6 +69,7 @@
 int boot_mapsize;
 #ifdef CONFIG_PPC_PMAC
 unsigned long agp_special_page;
+EXPORT_SYMBOL(agp_special_page);
 #endif
 
 extern char _end[];