[POWERPC] Limit range of __init_ref_ok somewhat

This patch introduces zalloc_maybe_bootmem and uses it so that we don't
have to mark a whole (largish) routine as __init_ref_ok.

Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Paul Mackerras <paulus@samba.org>
diff --git a/include/asm-powerpc/system.h b/include/asm-powerpc/system.h
index f7879fc..d10e99b 100644
--- a/include/asm-powerpc/system.h
+++ b/include/asm-powerpc/system.h
@@ -190,6 +190,7 @@
 extern unsigned long klimit;
 
 extern void *alloc_maybe_bootmem(size_t size, gfp_t mask);
+extern void *zalloc_maybe_bootmem(size_t size, gfp_t mask);
 
 extern int powersave_nap;	/* set if nap mode can be used in idle loop */