Document the need to call psa_crypto_init() with USE_PSA_CRYPTO

When MBEDTLS_USE_PSA_CRYPTO is enabled, the application must call
psa_crypto_init() before directly or indirectly calling cipher or PK code
that will use PSA under the hood. Document this explicitly for some
functions.

To avoid clutter, this commit only documents the need to call
psa_crypto_init() in common, non-obvious cases: parsing a public key
directly or via X.509, or setting up an SSL context. Functions that are
normally only called after such a function (for example, using an already
constructed PK object), or where the need for PSA is obvious because they
take a key ID as argument, do not need more explicit documentaion.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/include/mbedtls/x509_crl.h b/include/mbedtls/x509_crl.h
index 49bbf61..62694ae 100644
--- a/include/mbedtls/x509_crl.h
+++ b/include/mbedtls/x509_crl.h
@@ -107,6 +107,10 @@
 /**
  * \brief          Parse a DER-encoded CRL and append it to the chained list
  *
+ * \note           If #MBEDTLS_USE_PSA_CRYPTO is enabled, the PSA crypto
+ *                 subsystem must have been initialized by calling
+ *                 psa_crypto_init() before calling this function.
+ *
  * \param chain    points to the start of the chain
  * \param buf      buffer holding the CRL data in DER format
  * \param buflen   size of the buffer
@@ -121,6 +125,10 @@
  *
  * \note           Multiple CRLs are accepted only if using PEM format
  *
+ * \note           If #MBEDTLS_USE_PSA_CRYPTO is enabled, the PSA crypto
+ *                 subsystem must have been initialized by calling
+ *                 psa_crypto_init() before calling this function.
+ *
  * \param chain    points to the start of the chain
  * \param buf      buffer holding the CRL data in PEM or DER format
  * \param buflen   size of the buffer
@@ -136,6 +144,10 @@
  *
  * \note           Multiple CRLs are accepted only if using PEM format
  *
+ * \note           If #MBEDTLS_USE_PSA_CRYPTO is enabled, the PSA crypto
+ *                 subsystem must have been initialized by calling
+ *                 psa_crypto_init() before calling this function.
+ *
  * \param chain    points to the start of the chain
  * \param path     filename to read the CRLs from (in PEM or DER encoding)
  *