mips: disable caches in bootblock startup code

Until proper MIPS cache management is available it is necessary to
disable data and instruction caches, otherwise code placed in memory
stays in data cache and is not available for instruction fetched.

BRANCH=none
BUG=chrome-os-partner:31438,chrome-os-partner:34127
TEST=coreboot loading rombase and rambase now succeeds.

Change-Id: I4147e1325edc0b9bb951cd7ce18d5f104f3eaec0
Signed-off-by: Stefan Reinauer <reinauer@chromium.org>
Original-Commit-Id: 93d5bfa1d0
Original-Change-Id: Ib195ed6e5f08ccaa6bbe3325c2199171bfb63b88
Original-Signed-off-by: Vadim Bendebury <vbendeb@chromium.org>
Original-Reviewed-on: https://chromium-review.googlesource.com/232191
Original-Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: http://review.coreboot.org/9569
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <pgeorgi@google.com>

src/arch/mips/bootblock.S

@@ -36,6 +36,16 @@ _start:
 	bne	$t0, $t1, 1b
 	addi	$t0, $t0, 4
 
+	/*
+	 * Disable caches for now, proper cache management is coming soon.
+	 * http://crosbug.com/p/34127
+	 */
+	mfc0	$t0, $16
+	li	$t1, -8
+	and	$t0, $t0, $t1
+	ori	$t0, $t0, 2
+	mtc0	$t0, $16
+
 	/* Run main */
 	b	main