M263: Fix mbedmicro-rtos-mbed-systimer/Wake up from deep sleep failing

This test requires total latency (tot = h/w + s/w) (wakeup from deepsleep) be
under 1ms. To check the issue, measure total latency on Nuvoton targets:

TARGET      EXP(us)     EXP+TOL(us) ACT(us)
NANO130     42000       43000       42939
NUC472      42000       43000       42236
M453        42000       43000       43274
M487        42000       43000       42877
M2351       42000       43000       43213

Checking h/w spec, h/w latency (wakeup time from normal power-down mode) on
M487/M2351 is just 1us (n/a on other targets). S/W latency plays the major
part here.

S/W latency relies on system performance. On Nuvoton targets, 'LPTICKER_DELAY_TICKS'
possibly complicates the test. Anyway, to pass the test, add extra 1ms latency
(deep-sleep-latency) in targets.json for Nuvoton targets.

targets/targets.json

@@ -9093,7 +9093,10 @@
         "release_versions": ["5"],
         "device_name": "M263KIAAE",
         "bootloader_supported": true,
-        "tickless-from-us-ticker": true,
+        "overrides": {
+            "deep-sleep-latency": 1,
+            "tickless-from-us-ticker": true
+        },
         "forced_reset_timeout": 3
     },    
     "__build_tools_metadata__": {