mx31: Fix boot hang by avoiding vector relocation

Since commit 3ff46cc4 ("arm: relocate the exception vectors") mx31
does not boot anymore.

Add a specific relocate_vectors macro that skips the vector relocation, as the
i.MX31 SoC does not provide RAM at the high vectors address (0xFFFF0000), and
(0x00000000) maps to ROM.

This allows mx31 to boot again.

Cc: Anatolij Gustschin <agust@denx.de>
Cc: Magnus Lilja <lilja.magnus@gmail.com>
Signed-off-by: NFabio Estevam <fabio.estevam@freescale.com>

arch/arm/cpu/arm1136/mx31/Makefile

@@ -8,3 +8,7 @@
 obj-y	+= generic.o
 obj-y	+= timer.o
 obj-y	+= devices.o
+
+ifndef CONFIG_SPL_BUILD
+obj-y  += relocate.o
+endif

arch/arm/cpu/arm1136/mx31/relocate.S

+/*
+ *  relocate - i.MX31-specific vector relocation
+ *
+ *  Copyright (c) 2013  Albert ARIBAUD <albert.u.boot@aribaud.net>
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+#include <linux/linkage.h>
+
+/*
+ * The i.MX31 SoC is very specific with respect to exceptions: it
+ * does not provide RAM at the high vectors address (0xFFFF0000),
+ * thus only the low address (0x00000000) is useable; but that is
+ * in ROM, so let's avoid relocating the vectors.
+ */
+	.section	.text.relocate_vectors,"ax",%progbits
+
+ENTRY(relocate_vectors)
+
+	bx	lr
+
+ENDPROC(relocate_vectors)