crypto: Add mbedtls-psa as a submodule

mbedtls-psa contains an implementation of libmbedcrypto, including the PSA
Crypto API.
diff --git a/tests/scripts/run-test-suites.pl b/tests/scripts/run-test-suites.pl
index 6fe6abf..4e57658 100755
--- a/tests/scripts/run-test-suites.pl
+++ b/tests/scripts/run-test-suites.pl
@@ -41,8 +41,8 @@
 die "$0: no test suite found\n" unless @suites;
 
 # in case test suites are linked dynamically
-$ENV{'LD_LIBRARY_PATH'} = '../library';
-$ENV{'DYLD_LIBRARY_PATH'} = '../library';
+$ENV{'LD_LIBRARY_PATH'} = '../library:../crypto/library';
+$ENV{'DYLD_LIBRARY_PATH'} = '../library:../crypto/library';
 
 my $prefix = $^O eq "MSWin32" ? '' : './';