clk: zynq: Leave debug clocks in bootup state

Make sure debug clocks stay enabled if the bootloader enabled them.
Otherwise debug HW may crash due to bus-hangs caused by stopped clocks.

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