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/library/x509_csr.c b/library/x509_csr.c
index 5463f8a..0a5d2cb 100644
--- a/library/x509_csr.c
+++ b/library/x509_csr.c
@@ -323,6 +323,7 @@
 }
 #endif /* MBEDTLS_FS_IO */
 
+#if defined(MBEDTLS_X509_INFO)
 #define BEFORE_COLON    14
 #define BC              "14"
 /*
@@ -367,6 +368,7 @@
 
     return( (int) ( size - n ) );
 }
+#endif /* MBEDTLS_X509_INFO */
 
 /*
  * Initialize a CSR