Add crypto_deinit function for crypto_backend module

Bootloader needs to have a mechanism to de-initialize crypto, in case some HW accelerator
is being used. This adds the needed function for it

Signed-off-by: Jukka Laitinen <jukkax@ssrc.tii.ae>

src/drivers/sw_crypto/crypto.c

@@ -151,6 +151,10 @@ void crypto_init()
 	clear_key_cache();
 }
 
+void crypto_deinit()
+{
+}
+
 crypto_session_handle_t crypto_open(px4_crypto_algorithm_t algorithm)
 {
 	crypto_session_handle_t ret;