gpu: fix separate alpha blending on swizzled render targets

Co-authored-by: Çağatay Güçlü <33038942+defektu@users.noreply.github.com>

src/graphics/host_gpu/renderer/pipeline/blendMapping.h

@@ -15,6 +15,7 @@ struct ColorComponentMapping;
 enum class BlendMappingSupport {
 	Direct,
 	SourceAlpha, // Requires logical alpha in the second blend source.
+	SourceAlphaOne, // Source alpha for RGB, one for alpha, with a shared destination equation.
 	Unsupported,
 };