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

Commit 002741ae 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: NWolfgang Denk <wd@denx.de>

include/asm-ppc/mmu.h

@@ -504,7 +504,7 @@ extern int num_tlb_entries;
 #endif
 #endif
 
-#ifdef CONFIG_MPC83xx
+#ifdef CONFIG_E300
 #define LAWAR_EN		0x80000000
 #define LAWAR_SIZE		0x0000003F