M2351: Refine MBED_TZ_DEFAULT_ACCESS placement

1.  On M2351, SYS/CLK registers are hard-wired to secure. Define MBED_TZ_DEFAULT_ACCESS to 1 so that all non-secure user threads have access to call secure functions to control these registers.
2.  MBED_TZ_DEFAULT_ACCESS is only meaningful for non-secure target. Define it only for non-secure target in targets.json.
3.  On TFM target, MBED_TZ_DEFAULT_ACCESS has defined in mbed_lib.json. Avoid duplicate definition which IAR assembler doesn't allow.

Author: ccli8

targets/targets.json

@@ -12544,7 +12544,6 @@
         "OUTPUT_EXT": "hex",
         "macros": [
             "MBED_FAULT_HANDLER_DISABLED",
-            "MBED_TZ_DEFAULT_ACCESS=1",
             "LPTICKER_DELAY_TICKS=4"
         ],
         "is_disk_virtual": true,
@@ -12683,7 +12682,6 @@
             "NU_PREBUILD_SECURE"
         ],
         "macros_add": [
-            "MBED_TZ_DEFAULT_ACCESS=1",
             "CMSIS_NVIC_VIRTUAL",
             "MBEDTLS_PSA_CRYPTO_C"
         ],