Fix: Allow target size restriction for LPC55S69

The build tool uses the sector size found in the CMSIS Pack to determine if
the size that can be specified by `target.restrict_size` is enough to fit
all the parts of a given binary. See `target.restrict_size` documentation
in the Mbed OS manual for more information.

The sector size found in the CMSIS Pack is overriden to allow the build
tool to accurately make the decision.

The target's sectors in the CMSIS Pack are defined in 32KB pages.
However, you can erase pages at the 512 byte level.

This commit changes defined sector erase size to 512 bytes instead of
32 Kilobytes.

targets/targets.json

@@ -2058,7 +2058,8 @@
         "detect_code": ["0236"],
         "device_name": "LPC55S69JBD100",
         "release_versions": ["5"],
-        "program_cycle_s": 10
+        "program_cycle_s": 10,
+        "sectors": [[0,512]]
     },
     "LPC55S69_NS": {
         "inherits": ["NSPE_Target", "LPC55S69"],