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/arch/arm/boot.c

@@ -25,3 +25,8 @@ void arch_prog_run(struct prog *prog)
 	doit = prog_entry(prog);
 	doit(prog_entry_arg(prog));
 }
+
+int arch_supports_bounce_buffer(void)
+{
+	return 0;
+}