Nuvoton: Add COMPONENT_FLASHIAP support

Some Nuvoton targets support DEVICE_FLASH but their corresponding COMPONENT_FLASHIAP
supports are not enabled. Enable them:

NUMAKER_PFM_M453
NUMAKER_PFM_M2351

targets/targets.json

@@ -7425,6 +7425,7 @@
             "FLASH",
             "MPU"
         ],
+        "components_add": ["FLASHIAP"],
         "release_versions": ["2", "5"],
         "device_name": "M453VG6AE",
         "bootloader_supported": true,
@@ -8091,6 +8092,7 @@
             "FLASH",
             "MPU"
         ],
+        "components_add": ["FLASHIAP"],
         "detect_code": ["1305"],
         "release_versions": ["5"],
         "device_name": "M2351KIAAEES",