powerpc/ppc476: Disable BTAC

This patch disables the branch target address CAM which under specific
circumstances may cause the processor to skip execution of 1-4
instructions. This fixes IBM Erratum #47.
Signed-off-by: Alistair Popple <alistair@popple.id.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/kernel/head_44x.S

@@ -1210,10 +1210,12 @@ clear_utlb_entry:
 
 	/* We configure icbi to invalidate 128 bytes at a time since the
 	 * current 32-bit kernel code isn't too happy with icache != dcache
-	 * block size
+	 * block size. We also disable the BTAC as this can cause errors
+	 * in some circumstances (see IBM Erratum 47).
 	 */
 	mfspr	r3,SPRN_CCR0
 	oris	r3,r3,0x0020
+	ori	r3,r3,0x0040
 	mtspr	SPRN_CCR0,r3
 	isync