Add missing include path to visual C script

We need to include from both tests/include and framework/tests/include.
Update scripts/generate_visualc_files.pl to re-add tests/include, which
had previously been replaced with framework/tests/include.

Signed-off-by: David Horstmann <david.horstmann@arm.com>
diff --git a/scripts/generate_visualc_files.pl b/scripts/generate_visualc_files.pl
index c0fddbe..76a6c32 100755
--- a/scripts/generate_visualc_files.pl
+++ b/scripts/generate_visualc_files.pl
@@ -55,6 +55,7 @@
     tf-psa-crypto/drivers/everest/include/everest
     tf-psa-crypto/drivers/everest/include/everest/vs2013
     tf-psa-crypto/drivers/everest/include/everest/kremlib
+    tests/include
     framework/tests/include
 );
 my $include_directories = join(';', map {"../../$_"} @include_directories);