arm: zynq: Add SLCR support with system reset

The patch provides slcr base address initialization support
and a support to reset the cpu through slcr driver,
hence removed the reset_cpu() from board.c.

Signed-off-by: Jagannadha Sutradharudu Teki <jaganna@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>