zynq: Move static clock names into separate array

The clock names are static and correspond to the clock id. Separate
them from the dynamic filled clock array.

Signed-off-by: Stefan Herbrechtsmeier <stefan.herbrechtsmeier@weidmueller.com>
Reviewed-by: Michal Simek <michal.simek@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>