arm: zynq: Add smp_twd timer

The zynq has a Cortex-A9 with the corresponding smp_twd timers. Use them.

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