tests: disable watchdog for sam_e70 in test kernel/critical

Wrong configuration of a watchdog for sam_e70_xplained_board caused
endless reboot loop. It seems that problem caused by a watchdog.
I created a new config for the sam_e70_xplained hardware board
like in master branch.

Signed-off-by: Maksim Masalski <maksim.masalski@intel.com>