Update TLS1.2 dependencies description in mbedtls_config.h

It is possible to use it without MBEDTLS_SHAXXX defines and USE_PSA_CRYPTO
instead.
Signed-off-by: Andrzej Kurek <andrzej.kurek@arm.com>
diff --git a/include/mbedtls/mbedtls_config.h b/include/mbedtls/mbedtls_config.h
index e1821f7..fd2391d 100644
--- a/include/mbedtls/mbedtls_config.h
+++ b/include/mbedtls/mbedtls_config.h
@@ -1493,7 +1493,12 @@
  * Enable support for TLS 1.2 (and DTLS 1.2 if DTLS is enabled).
  *
  * Requires: MBEDTLS_SHA1_C or MBEDTLS_SHA256_C or MBEDTLS_SHA512_C
- *           (Depends on ciphersuites)
+ *           (Depends on ciphersuites) when MBEDTLS_USE_PSA_CRYPTO
+ *           is not defined, PSA_WANT_ALG_SHA_1 or PSA_WANT_ALG_SHA_256 or
+ *           PSA_WANT_ALG_SHA_512 when MBEDTLS_USE_PSA_CRYPTO is defined.
+ *
+ * \warning If building without MBEDTLS_MD_C, you must call psa_crypto_init()
+ * before doing any TLS operation.
  *
  * Comment this macro to disable support for TLS 1.2 / DTLS 1.2
  */