ppc64: Fix module exports for G5

Hi !

Some stuffs in ppc_ksyms.c where still #ifdef CONFIG_PPC_PSERIES, which is no longer set for PowerMac-only configs. Change them to depend on CONFIG_PPC_MULTIPLATFORM for now. Later on, a bunch of these will be just gone since those are mostly deprecated functions and I'll move the exports close to the actual functions.

===== arch/ppc64/kernel/ppc_ksyms.c 1.44 vs edited =====

@@ -136,7 +136,7 @@
 
 EXPORT_SYMBOL(ppc_md);
 
-#ifdef CONFIG_PPC_PSERIES
+#ifdef CONFIG_PPC_MULTIPLATFORM
 EXPORT_SYMBOL(find_devices);
 EXPORT_SYMBOL(find_type_devices);
 EXPORT_SYMBOL(find_compatible_devices);