arm64: zynqmp: Disable WDT_CDNS driver by default

Do not enable watchdog driver in default zynqmp configuration. The reason
is that not all distributions are handling watchdog properly and then
expires and system resets. If someone needs watchdog in their design please
enable it by hand.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>