die() when attempting to use bounce buffer on non-i386.

Only i386 has code to support bounce buffer. For others coreboot
would silently discard part of binary which doesn't work and is a hell to debug.

Instead just die.

Change-Id: I37ae24ea5d13aae95f9856a896700a0408747233
Signed-off-by: Vladimir Serbinenko <phcoder@gmail.com>
Reviewed-on: https://review.coreboot.org/13750
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

src/lib/selfboot.c

@@ -114,6 +114,9 @@ static int relocate_segment(unsigned long buffer, struct segment *seg)
 	if (!overlaps_coreboot(seg))
 		return 0;
 
+	if (!arch_supports_bounce_buffer())
+		die ("bounce buffer not supported");
+
 	start = seg->s_dstaddr;
 	middle = start + seg->s_filesz;
 	end = start + seg->s_memsz;