Add RNG params to private key parsing

This is necessary for the case where the public part of an EC keypair
needs to be computed from the private part - either because it was not
included (it's an optional component) or because it was compressed (a
format we can't parse).

This changes the API of two public functions: mbedtls_pk_parse_key() and
mbedtls_pk_parse_keyfile().

Tests and programs have been adapted. Some programs use a non-secure RNG
(from the test library) just to get things to compile and run; in a
future commit this should be improved in order to demonstrate best
practice.

Signed-off-by: Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com>
diff --git a/programs/ssl/ssl_client2.c b/programs/ssl/ssl_client2.c
index 98a3048..6501c49 100644
--- a/programs/ssl/ssl_client2.c
+++ b/programs/ssl/ssl_client2.c
@@ -1548,12 +1548,12 @@
     else
 #if defined(MBEDTLS_FS_IO)
     if( strlen( opt.key_file ) )
-        ret = mbedtls_pk_parse_keyfile( &pkey, opt.key_file, opt.key_pwd );
+        ret = mbedtls_pk_parse_keyfile( &pkey, opt.key_file, opt.key_pwd, rng_get, &rng );
     else
 #endif
         ret = mbedtls_pk_parse_key( &pkey,
                 (const unsigned char *) mbedtls_test_cli_key,
-                mbedtls_test_cli_key_len, NULL, 0 );
+                mbedtls_test_cli_key_len, NULL, 0, rng_get, &rng );
     if( ret != 0 )
     {
         mbedtls_printf( " failed\n  !  mbedtls_pk_parse_key returned -0x%x\n\n",