Nuvoton: Remove TRNG support

These targets below just support PRNG, not real TRNG. They cannot annouce TRNG.

-   NUMAKER_PFM_NUC472
-   NUMAKER_PFM_M487
-   NUMAKER_IOT_M487

On targets without TRNG, to run mbedtls applications which require entropy source,
there are two alternatives to TRNG:

-   Custom entropy source:
    Define MBEDTLS_ENTROPY_HARDWARE_ALT and provide custom mbedtls_hardware_poll(...)
-   NV seed:
    1.  Define MBEDTLS_ENTROPY_NV_SEED
    2.  Define MBEDTLS_PLATFORM_NV_SEED_READ_MACRO/MBEDTLS_PLATFORM_NV_SEED_WRITE_MACRO and provide custom mbedtls_nv_seed_read(...)/mbedtls_nv_seed_write(...).
    3.  Don't define MBEDTLS_PSA_INJECT_ENTROPY. Meet mbedtls_psa_inject_entropy(...) undefined and then provide custom one, which must be compatible with mbedtls_nv_seed_read(...)/mbedtls_nv_seed_write(...) above.
    4.  For development, simulating partial provision process, inject entropy seed via mbedtls_psa_inject_entropy(...) pre-main.

Author: ccli8

targets/TARGET_NUVOTON/TARGET_M480/objects.h

@@ -1,5 +1,5 @@
 /* mbed Microcontroller Library
- * Copyright (c) 2015-2016 Nuvoton
+ * Copyright (c) 2015-2019 Nuvoton
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -118,10 +118,6 @@ struct pwmout_s {
     uint32_t pulsewidth_us;
 };
 
-struct trng_s {
-    uint8_t dummy;
-};
-
 struct can_s {
     CANName can;
     PinName pin_rd;

targets/TARGET_NUVOTON/TARGET_M480/trng_api.c

@@ -1,5 +1,5 @@
 /* mbed Microcontroller Library
- * Copyright (c) 2015-2016 Nuvoton
+ * Copyright (c) 2015-2019 Nuvoton
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -114,10 +114,6 @@ struct pwmout_s {
     uint32_t pulsewidth_us;
 };
 
-struct trng_s {
-    uint8_t dummy;
-};
-
 struct can_s {
 	CANName can;
     PinName pin_rd;

targets/TARGET_NUVOTON/TARGET_NUC472/objects.h

@@ -7980,7 +7980,6 @@
             "SPI",
             "SPISLAVE",
             "SPI_ASYNCH",
-            "TRNG",
             "CAN",
             "FLASH",
             "EMAC",
@@ -8629,7 +8628,6 @@
             "SPI",
             "SPISLAVE",
             "SPI_ASYNCH",
-            "TRNG",
             "FLASH",
             "CAN",
             "EMAC",