psa: programs: Add cipher example

Add `programs/psa/crypto_examples.c`. Update relevant Makefiles,
CMakeLists.txt, and .gitignore files.
diff --git a/programs/psa/crypto_examples.c b/programs/psa/crypto_examples.c
new file mode 100644
index 0000000..3a549ff
--- /dev/null
+++ b/programs/psa/crypto_examples.c
@@ -0,0 +1,4 @@
+int main( void )
+{
+    return( 0 );
+}