Refactor D3D11 shaders to reduce duplicated code

app/shaders/d3d11_video_pixel_end.hlsli

@@ -0,0 +1,13 @@
+min16float4 main(ShaderInput input) : SV_TARGET
+{
+    min16float3 yuv = min16float3(luminancePlane.Sample(theSampler, input.tex),
+                                  chrominancePlane.Sample(theSampler, input.tex));
+
+    // Subtract the YUV offset for limited vs full range
+    yuv -= offsets;
+
+    // Multiply by the conversion matrix for this colorspace
+    yuv = mul(yuv, cscMatrix);
+
+    return min16float4(yuv, 1.0);
+}