Rework type for verify chain

- create container with length + table
- make types public (will be needed in restart context)
diff --git a/include/mbedtls/x509_crt.h b/include/mbedtls/x509_crt.h
index 61a9124..eb929d7 100644
--- a/include/mbedtls/x509_crt.h
+++ b/include/mbedtls/x509_crt.h
@@ -142,6 +142,28 @@
 }
 mbedtls_x509write_cert;
 
+/**
+ * Item in a verification chain: cert and flags for it
+ */
+typedef struct {
+    mbedtls_x509_crt *crt;
+    uint32_t flags;
+} mbedtls_x509_crt_verify_chain_item;
+
+/**
+ * Max size of verification chain: end-entity + intermediates + trusted root
+ */
+#define MBEDTLS_X509_MAX_VERIFY_CHAIN_SIZE  ( MBEDTLS_X509_MAX_INTERMEDIATE_CA + 2 )
+
+/**
+ * Verification chain as built by \c mbedtls_crt_verify_chain()
+ */
+typedef struct
+{
+    mbedtls_x509_crt_verify_chain_item items[MBEDTLS_X509_MAX_VERIFY_CHAIN_SIZE];
+    size_t len;
+} mbedtls_x509_crt_verify_chain;
+
 #if defined(MBEDTLS_ECDSA_C) && defined(MBEDTLS_ECP_RESTARTABLE)
 
 /**