ppc: Rework some hard-coded BOOTCOMMANDS

There are an assortment of hard-coded CONFIG_BOOTCOMMAND options in some
board headers.  Rework these so that they do not add to the CONFIG
namespace.

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/include/configs/ids8313.h b/include/configs/ids8313.h
index b9d2fe3..d4f4910 100644
--- a/include/configs/ids8313.h
+++ b/include/configs/ids8313.h
@@ -279,7 +279,7 @@
 	"mtdparts=" CONFIG_MTDPARTS_DEFAULT "\0"				\
 	"\0"
 
-#define CONFIG_NFSBOOTCOMMAND						\
+#define NFSBOOTCOMMAND						\
 	"setenv rootdev /dev/nfs;"					\
 	"run setipargs;run addmtd;"					\
 	"tftp ${loadaddr} ${bootfile};"				\