[M252KG] Enlarge required deep sleep latency

This configuration is to pass wake-up from deep-sleep test such as mbedmicro-rtos-mbed-systimer.

Author: ccli8

targets/targets.json

@@ -8326,6 +8326,7 @@
         },
         "overrides": {
             "mpu-rom-end": "0x1fffffff",
+            "deep-sleep-latency": 1,
             "tickless-from-us-ticker": true
         },
         "inherits": ["Target"],