arch: arm: dts: k3-am642-phyboard-electra: Disable unused watchdogs in U-Boot

arch: arm: dts: k3-am642-phyboard-electra: Disable unused watchdogs in U-Boot

The watchdog driver probes all available watchdog devices.
This causes SMP boot errors when bringing up secondary CPUs.
In our setup, only a single watchdog is needed to monitor the
boot process until userspace or the OS takes over. Disable all
unnecessary watchdog devices in U-Boot to avoid conflicts
during CPU bring-up.

Signed-off-by: Wadim Egorov <w.egorov@phytec.de>