Reduce code size when mbedtls_x509_*_info() unused

Introduce MBEDTLS_X509_INFO to indicate the availability of the
mbedtls_x509_*_info() function and closely related APIs. When this is
not defined, also omit name and description from
mbedtls_oid_descriptor_t, and omit OID arrays, macros, and types that
are entirely unused. This saves several KB of code space.

Signed-off-by: Hanno Becker <hanno.becker@arm.com>
Signed-off-by: Chris Jones <christopher.jones@arm.com>
diff --git a/include/mbedtls/oid.h b/include/mbedtls/oid.h
index e4c697b..89b5fe8 100644
--- a/include/mbedtls/oid.h
+++ b/include/mbedtls/oid.h
@@ -441,8 +441,10 @@
 {
     const char *asn1;               /*!< OID ASN.1 representation       */
     size_t asn1_len;                /*!< length of asn1                 */
+#if defined(MBEDTLS_X509_INFO)
     const char *name;               /*!< official name (e.g. from RFC)  */
     const char *description;        /*!< human friendly description     */
+#endif
 } mbedtls_oid_descriptor_t;
 
 /**
@@ -582,6 +584,7 @@
 int mbedtls_oid_get_md_hmac( const mbedtls_asn1_buf *oid, mbedtls_md_type_t *md_hmac );
 #endif /* MBEDTLS_MD_C */
 
+#if defined(MBEDTLS_X509_INFO)
 /**
  * \brief          Translate Extended Key Usage OID into description
  *
@@ -591,6 +594,7 @@
  * \return         0 if successful, or MBEDTLS_ERR_OID_NOT_FOUND
  */
 int mbedtls_oid_get_extended_key_usage( const mbedtls_asn1_buf *oid, const char **desc );
+#endif
 
 /**
  * \brief          Translate certificate policies OID into description