Add config-default.h to test-ref-configs.pl

This commit adds the default upstream configuration to the set of
tests we run on CI, which was long overdue.

config-default is a copy of the Mbed TLS upstream config.h. It's
useful for two things: to compare our local changes to
include/mbedtls/config.h, and to test that we aren't breaking the
default upstream configuration.

Run a subset of the TLS tests that focus on exercising cryptographic
algorithms as used from TLS. Don't run the full set of TLS tests
because they're unlikely to be affected by changes in the PSA branch.

tests/scripts/test-ref-configs.pl

@@ -17,6 +17,10 @@ use warnings;
 use strict;
 
 my %configs = (
+    'config-default.h' => {
+        'opt' => '-f Default',
+        'compat' => '-m tls1_2 -V NO',
+    },
     'config-mini-tls1_1.h' => {
         'compat' => '-m tls1_1 -f \'^DES-CBC3-SHA$\|^TLS-RSA-WITH-3DES-EDE-CBC-SHA$\'',
     },