tests: Test crypto via the crypto submodule

Test the crypto implementation via tests from the Mbed Crypto submodule
instead of at the Mbed TLS top level.

The version test is the only test that is tested from both TLS and
Crypto, despite being entirely in libmbedcrypto. This is because the
test data is code-gen'd from the version updating script and the version
between Mbed TLS and Mbed Crypto don't necessarily always agree. The
test data must come from the top level module, as only the top level
module will have test data that matches the expected version.
diff --git a/Makefile b/Makefile
index 87b5a0c..a5b8b61 100644
--- a/Makefile
+++ b/Makefile
@@ -19,6 +19,9 @@
 
 tests: lib
 	$(MAKE) -C tests
+ifdef USE_CRYPTO_SUBMODULE
+	$(MAKE) CRYPTO_INCLUDES:="-I../../include -I../include" -C crypto/tests
+endif
 
 ifndef WINDOWS
 install: no_test
@@ -103,6 +106,9 @@
 
 check: lib tests
 	$(MAKE) -C tests check
+ifdef USE_CRYPTO_SUBMODULE
+	$(MAKE) CRYPTO_INCLUDES:="-I../../include -I../include" -C crypto/tests check
+endif
 
 test: check