Fix "ppc/85xx: Clean up use of LAWAR defines" breakage

Commit 002741ae86 modified include/asm-ppc/mmu.h such that the LAWAR_
defines were only enabled for the 83xx platform, but they are also
needed on MPC512x system. Enabling these for E300 systems seems thus
more appropriate.

Signed-off-by: Wolfgang Denk <wd@denx.de>
diff --git a/include/asm-ppc/mmu.h b/include/asm-ppc/mmu.h
index d516d91..ec22a50 100644
--- a/include/asm-ppc/mmu.h
+++ b/include/asm-ppc/mmu.h
@@ -504,7 +504,7 @@
 #endif
 #endif
 
-#ifdef CONFIG_MPC83xx
+#ifdef CONFIG_E300
 #define LAWAR_EN		0x80000000
 #define LAWAR_SIZE		0x0000003F