Add deprecated attribute to depracted functions

bindgen does add the deprecated attribute to deprecated functions.  This patch
manually adds the attributes libnitrokey’s deprecated functions.
Index: nitrokey-sys-rs/src/ffi.rs
===================================================================
--- nitrokey-sys-rs.orig/src/ffi.rs
+++ nitrokey-sys-rs/src/ffi.rs
@@ -212,6 +212,7 @@ extern "C" {
     #[doc = " deprecated in favor of NK_get_status_as_string."]
     #[doc = " @return string representation of the status or an empty string"]
     #[doc = "         if the command failed"]
+    #[deprecated(since = "3.5.0", note="use `NK_get_status_as_string` instead")]
     pub fn NK_status() -> *mut ::std::os::raw::c_char;
 }
 extern "C" {
@@ -498,6 +499,7 @@ extern "C" {
     pub fn NK_totp_set_time_soft(time: u64) -> ::std::os::raw::c_int;
 }
 extern "C" {
+    #[deprecated(since = "3.4.0", note="use `NK_totp_set_time_soft` instead")]
     pub fn NK_totp_get_time() -> ::std::os::raw::c_int;
 }
 extern "C" {
@@ -673,6 +675,7 @@ extern "C" {
     #[doc = " Storage only"]
     #[doc = " @param user_pin 20 characters User PIN"]
     #[doc = " @return command processing error code"]
+    #[deprecated(since = "3.6.0", note = "use `set_unencrypted_read_only_admin` instead")]
     pub fn NK_set_unencrypted_read_only(
         user_pin: *const ::std::os::raw::c_char,
     ) -> ::std::os::raw::c_int;
@@ -686,6 +689,7 @@ extern "C" {
     #[doc = " Storage only"]
     #[doc = " @param user_pin 20 characters User PIN"]
     #[doc = " @return command processing error code"]
+    #[deprecated(since = "3.6.0", note = "use `set_unencrypted_read_write_admin` instead")]
     pub fn NK_set_unencrypted_read_write(
         user_pin: *const ::std::os::raw::c_char,
     ) -> ::std::os::raw::c_int;