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>

arch/ppc/mm/init.c

@@ -69,6 +69,7 @@ int init_bootmem_done;
 int boot_mapsize;
 #ifdef CONFIG_PPC_PMAC
 unsigned long agp_special_page;
+EXPORT_SYMBOL(agp_special_page);
 #endif
 
 extern char _end[];