powerpc/47x: Make sure mcsr is cleared before enabling machine check interrupts

Clear the machine check syndrom register before enabling machine check
interrupts.  The initial state of the tlb can lead to parity errors being
flagged early after a cold boot.
Signed-off-by: NDave Kleikamp <shaggy@linux.vnet.ibm.com>
Signed-off-by: NJosh Boyer <jwboyer@linux.vnet.ibm.com>

arch/powerpc/kernel/head_44x.S

@@ -113,6 +113,10 @@ _ENTRY(_start);
 	stw	r5, 0(r4)	/* Save abatron_pteptrs at a fixed location */
 	stw	r6, 0(r5)
 
+	/* Clear the Machine Check Syndrome Register */
+	li	r0,0
+	mtspr	SPRN_MCSR,r0
+
 	/* Let's move on */
 	lis	r4,start_kernel@h
 	ori	r4,r4,start_kernel@l