On ARMv7 the exception vectors inside the barebox binary are used directly
by remapping the vectors base through the VBAR register. While VBAR allows
to remap the exception vectors freely, it still imposes a minimum alignment
of 32 byte, as the lower bits are treated as the exception vector offset.
Enforce this alignment inside the barebox binary.

Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>