drivers: watchdog: wdt_dw: bug fix and modify conditional macro check

clearing interrupt flag will not assert the system reset as per IP spec,
so interrupt flag should not be cleared in isr

use #if macro check directly with DT_ANY_INST_HAS_PROP_STATUS_OKAY for
interrupt

Signed-off-by: Balsundar Ponnusamy <balsundar.ponnusamy@intel.com>