psa: programs: Add cipher example

Add `programs/psa/crypto_examples.c`. Update relevant Makefiles,
CMakeLists.txt, and .gitignore files.
diff --git a/programs/CMakeLists.txt b/programs/CMakeLists.txt
index 4cdae78..661b120 100644
--- a/programs/CMakeLists.txt
+++ b/programs/CMakeLists.txt
@@ -1,6 +1,7 @@
 add_subdirectory(aes)
 add_subdirectory(hash)
 add_subdirectory(pkey)
+add_subdirectory(psa)
 add_subdirectory(random)
 add_subdirectory(ssl)
 add_subdirectory(test)