arm64: zynqmp: Add DT description for si5328 for zcu102/zcu106

Origin DT binding just specify driver but wasn't aligned with DT binding
which came later. Extend description for zcu102 and zcu106 to cover latest
binding.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@amd.com>
Link: https://lore.kernel.org/r/db66a4bb501183ffbd033da4dd263afdb214f8ec.1652262769.git.michal.simek@amd.com