ARM: zynq: DT: Migrate UART to Cadence binding

The Zynq UART is Cadence IP and the driver has been renamed accordingly.
Migrate the DT to use the new binding for the UART driver.

Signed-off-by: Soren Brinkmann <soren.brinkmann@xilinx.com>
Acked-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
Acked-by: Rob Herring <robh@kernel.org>
Tested-by: Michal Simek <michal.simek@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>