Implement BSD Service (#54)

* Implement BSD Service

- Implementation of bsd:s & bsd:u.
- Adding an EndianSwap class.

* Corrections #1

* Correction2

Ryujinx.Core/OsHle/Utilities/EndianSwap.cs

@@ -0,0 +1,7 @@
+namespace Ryujinx.Core.OsHle.Utilities
+{
+    static class EndianSwap
+    {
+        public static short Swap16(short Value) => (short)(((Value >> 8) & 0xff) | (Value << 8));
+    }
+}