[nrf fromtree] tests: net: socket: tls: Optimize mbed TLS configuration

All handshakes within the test suite are PSK-based, therefore it's only
needed to enable MBEDTLS_CIPHERSUITE_TLS_PSK_WITH_AES_256_CBC_SHA384,
MBEDTLS_CIPHERSUITE_TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256 is not needed
or used in tests so it only increases the overall image size.

For the few tests verifying the certificate validation, it's enough to
enable X509 certificate parsing and a few dependencies.

Signed-off-by: Robert Lubos <robert.lubos@nordicsemi.no>
(cherry picked from commit 9f299be)

Author: rlubos

tests/net/socket/tls/prj.conf

@@ -52,4 +52,9 @@ CONFIG_MBEDTLS_HEAP_SIZE=30000
 CONFIG_MBEDTLS_SSL_DTLS_CONNECTION_ID=y
 CONFIG_MBEDTLS_PSA_KEY_SLOT_COUNT=32
 CONFIG_MBEDTLS_CIPHERSUITE_TLS_PSK_WITH_AES_256_CBC_SHA384=y
-CONFIG_MBEDTLS_CIPHERSUITE_TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256=y
+
+# For tests verifying certificate validation
+CONFIG_MBEDTLS_X509_CRT_PARSE_C=y
+CONFIG_PSA_WANT_KEY_TYPE_RSA_PUBLIC_KEY=y
+CONFIG_PSA_WANT_KEY_TYPE_RSA_KEY_PAIR_IMPORT=y
+CONFIG_PSA_WANT_ALG_RSA_PKCS1V15_SIGN=y