arm64: zynqmp: Disable watchdog by default for virt platform

Disable watchdog based on request in past that not all Linux rootfs have
proper utilities ready to service it. Enable it if your rootfs have proper
watchdog handling.

Signed-off-by: Michal Simek <michal.simek@amd.com>
Link: https://lore.kernel.org/r/62dfc08f32635abee42feab26aaa9efed52134c0.1665567328.git.michal.simek@amd.com