adding two new ddk header, the info are base/got from windows xp ddk kit version 3790.1830

svn path=/trunk/; revision=24813

reactos/include/ddk/dxapi.h

@@ -0,0 +1,4 @@
+
+ULONG DxApiGetVersion();
+ULONG DxApi( IN ULONG dwFunctionNum,IN PVOID lpvInBuffer, IN ULONG cbInBuffer, 
+             IN PVOID lpvOutBuffer, IN ULONG cbOutBuffer);

reactos/include/ddk/fltsafe.h

@@ -0,0 +1,19 @@
+
+struct FLOATSAFE
+{
+   KFLOATING_SAVE FloatSave;
+   NTSTATUS ntStatus;
+
+   FLOATSAFE::FLOATSAFE(void)
+   {
+     ntStatus = KeSaveFloatingPointState(&FloatSave);
+   }
+
+   FLOATSAFE::~FLOATSAFE(void)
+   {
+     if (NT_SUCCESS(ntStatus))
+     {
+        KeRestoreFloatingPointState(&FloatSave);
+     }
+   }
+};