[POWERPC] Make sure initrd and dtb sections get into zImage correctly

The "wrapper" script was using the wrong names for the initrd and
dtb (device-tree blob) sections.  This fixes it, and also ensures
the symbols for the start and end of the dtb get defined correctly.

Signed-off-by: Paul Mackerras <paulus@samba.org>
diff --git a/arch/powerpc/boot/wrapper b/arch/powerpc/boot/wrapper
index eab7318..b5fb1fe 100755
--- a/arch/powerpc/boot/wrapper
+++ b/arch/powerpc/boot/wrapper
@@ -179,11 +179,11 @@
 fi
 
 if [ -n "$initrd" ]; then
-    addsec $tmp "$initrd" initrd
+    addsec $tmp "$initrd" $isection
 fi
 
 if [ -n "$dtb" ]; then
-    addsec $tmp "$dtb" dtb
+    addsec $tmp "$dtb" .kernel:dtb
 fi
 
 if [ "$platform" != "miboot" ]; then