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: Fabio Estevam <fabio.estevam@freescale.com>