soc: defconfig: Enable WDT for ATMEL SAM MCUs

In Atmel SAM Family of MCUs, the watchdog is enabled by default at boot.
The watchdog once disabled, cannot be re-enabled back without a reset.
Hence disabling the Watchdog needs to be handled via the Watchdog driver.

Tested on Atmel SAMV71 Xplained Ultra Evaluation Kit.

Jira: ZEP-1684

Change-Id: I5682c3f007a846b064b8d16abf0d9b67d4c8e7d6
Signed-off-by: Souvik K Chakravarty <souvik.k.chakravarty@intel.com>