ppc: Conditionally compile bat_rw.c

Only a few PPC boards actually use the common BAT manipulation
functions, so only compile it for them.

Signed-off-by: Peter Tyser <ptyser@xes-inc.com>
diff --git a/include/configs/Alaska8220.h b/include/configs/Alaska8220.h
index 576aa74..85b68be 100644
--- a/include/configs/Alaska8220.h
+++ b/include/configs/Alaska8220.h
@@ -31,6 +31,7 @@
 #define CONFIG_MPC8220		1
 #define CONFIG_ALASKA8220	1	/* ... on Alaska board	*/
 
+#define CONFIG_BAT_RW		1	/* Use common BAT rw code */
 #define CONFIG_HIGH_BATS	1	/* High BATs supported */
 
 /* Input clock running at 30Mhz, read Hid1 for the CPU multiplier to