Replace legacy RNG in sample programs

[davidhorstmann-arm]

Part of implementing #9904

Replace the legacy random number generation with psa_generate_random() in the following programs:

• x509/cert_app.c
• x509/cert_req.c
• x509/cert_write.c
• pkey/pk_sign.c
• pkey/rsa_sign_pss.c
• fuzz/fuzz_dtlsclient.c
• fuzz/fuzz_privkey.c
• fuzz/fuzz_server.c
• fuzz/fuzz_dtlsserver.c
• fuzz/fuzz_client.c
• fuzz/common.c
• ssl/ssl_server.c
• ssl/dtls_server.c
• ssl/ssl_mail_client.c
• ssl/ssl_client1.c
• ssl/mini_client.c
• ssl/ssl_test_lib.c
• ssl/dtls_client.c
• ssl/ssl_pthread_server.c
• ssl/ssl_fork_server.c

Currently these programs call the Mbed TLS legacy entropy and DRBG functions to generate random data. Replace all of that setup with a simple call to psa_generate_random() (and add a call to psa_crypto_init() if required).

Note: where the random generation function is passed as a callback, you may need to use the mbedtls_psa_get_random() wrapper.

This task is done when none of the listed programs use the legacy API for random number generation (and they all work). Manual testing may be required as we don't have automated tests for all of the programs.

Estimate: 10 Ideal Engineering Hours