include: Add D3D11_KEEP_* constants.

include/d3d11.idl

@@ -103,6 +103,9 @@ const INT D3D11_VIEWPORT_BOUNDS_MIN          = -32768;
 const UINT D3D11_VIEWPORT_AND_SCISSORRECT_MAX_INDEX = 15;
 const UINT D3D11_VIEWPORT_AND_SCISSORRECT_OBJECT_COUNT_PER_PIPELINE = 16;
 
+const UINT D3D11_KEEP_RENDER_TARGETS_AND_DEPTH_STENCIL = 0xffffffff;
+const UINT D3D11_KEEP_UNORDERED_ACCESS_VIEWS           = 0xffffffff;
+
 const UINT D3D11_SHADER_MAJOR_VERSION        = 5;
 const UINT D3D11_SHADER_MAX_INSTANCES        = 65535;
 const UINT D3D11_SHADER_MAX_INTERFACES       = 253;