mips: fix bootblock stack definitions

Bootblock stack on Danube should be SRAM and defined separately from
the rest of the coreboot stack. The actual coreboot stack will be
defined later.

The top of the stack should be above the bottom, as the stack grows
towards lower addresses.

BUG=chrome-os-partner:31438
TEST=ran bootblock on simulator under codescape, observed stack
     properly initialized.

Change-Id: I43d2bae5f85a09a95ca0103b253399bd92555aef
Signed-off-by: Patrick Georgi <pgeorgi@chromium.org>
Original-Commit-Id: e02724cb4b30990ebaa631dabb45917af29d6437
Original-Change-Id: I3c37c8b5a1c0e7fd19411558a8f6d899fc283191
Original-Signed-off-by: Vadim Bendebury <vbendeb@chromium.org>
Original-Reviewed-on: https://chromium-review.googlesource.com/218732
Original-Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: http://review.coreboot.org/8767
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>

src/arch/mips/bootblock.inc

@@ -23,13 +23,13 @@
 .globl _start
 _start:
 	/* Set the stack pointer */
-	li	$sp, CONFIG_STACK_TOP
+	li	$sp, CONFIG_BOOTBLOCK_STACK_TOP
 
 	/*
 	 * Initialise the stack to a known value, used later to check for
 	 * overflow.
 	 */
-	li	$t0, CONFIG_STACK_BOTTOM
+	li	$t0, CONFIG_BOOTBLOCK_STACK_BOTTOM
 	addi	$t1, $sp, -4
 	li	$t2, 0xdeadbeef
 1:	sw	$t2, 0($t0)