ppc/85xx: Ensure that MAS8 is zero when writing TLB entries.

Its reset value is random, and we sometimes read uninitialized TLB
arrays.  Make sure that we don't retain MAS8 from reading such an entry
if the VF bit in MAS8 is set, attempts to use the mapping will trap.

Signed-off-by: Scott Wood <scottwood@freescale.com>
diff --git a/cpu/mpc85xx/start.S b/cpu/mpc85xx/start.S
index eaed0e0..7a23b4f 100644
--- a/cpu/mpc85xx/start.S
+++ b/cpu/mpc85xx/start.S
@@ -156,6 +156,10 @@
 	mtspr	MCSR,r0			/* machine check syndrome register */
 	mtxer	r0			/* clear integer exception register */
 
+#ifdef CONFIG_SYS_BOOK3E_HV
+	mtspr	MAS8,r0			/* make sure MAS8 is clear */
+#endif
+
 	/* Enable Time Base and Select Time Base Clock */
 	lis	r0,HID0_EMCP@h		/* Enable machine check */
 #if defined(CONFIG_ENABLE_36BIT_PHYS)