arm: zynq: slcr: Clean up #defines

Use a common naming scheme for register offset #defines:
Some of those used a '_OFFSET' suffix to distinguish them from others.
This scheme is used for all register offsets now.

Separate the register offset #defines from others and sort them in
increasing order.

Signed-off-by: Soren Brinkmann <soren.brinkmann@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>