arm: zynq: Add smp support

Zynq is dual core Cortex A9 which starts always
at zero. Using simple trampoline ensure long jump
to secondary_startup code.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Signed-off-by: Steffen Trumtrar <s.trumtrar@pengutronix.de>