nfp:user: Implement IUser (#714)

* nfp:user: Implement IUser

- Based on RE of sysmod FW 1.0 and 3.0 with help of https://github.com/switchbrew/libnx/ and https://reswitched.github.io/SwIPC/ifaces.html#nn::nfp::detail::IUser
- Accurate implementation of Initialize, AttachActivateEvent, AttachDeactivateEvent, GetState, GetDeviceState, GetNpadId and GetDeviceState.
- Implementation of Finalize and ListDevices (close #638).

* reorder private var

* fix nits

Ryujinx.HLE/HOS/Services/Nfc/Nfp/DeviceState.cs

@@ -0,0 +1,13 @@
+namespace Ryujinx.HLE.HOS.Services.Nfc.Nfp
+{
+    enum DeviceState
+    {
+        Initialized     = 0,
+        SearchingForTag = 1,
+        TagFound        = 2,
+        TagRemoved      = 3,
+        TagMounted      = 4,
+        Unavailable     = 5,
+        Finalized       = 6
+    }
+}