ARM64: zynqmp: Add u-boot,dm-pre-reloc to clk nodes

ARM64: zynqmp: Add u-boot,dm-pre-reloc to clk nodes

Serial driver is getting clk information via DT that's why
also clk node needs to have this flag.

Different behavior was introduced by:
"dm: Use dm_scan_fdt_dev() directly where possible"
(sha1: 911954859d6dece49c3e4835faea004cfe392506)
where simple-bus driver starts to call dm_scan_fdt_dev() which has
additional logic around pre_reloc_only parameter which exclude
clk nodes.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Reviewed-by: Simon Glass <sjg@chromium.org>