GS: Fix AA1 coverage regression on sw and cleanup.

pcsx2/GS/Renderers/HW/GSRendererHW.cpp

@@ -10473,6 +10473,5 @@ std::size_t GSRendererHW::ComputeDrawlistGetSize(float scale)
 
 bool GSRendererHW::IsCoverageAlphaSupported()
 {
-	return IsCoverageAlpha() && g_gs_device->Features().aa1 &&
-	       (m_vt.m_primclass == GS_LINE_CLASS || m_vt.m_primclass == GS_TRIANGLE_CLASS);
+	return IsCoverageAlpha() && g_gs_device->Features().aa1;
 }

pcsx2/GS/Renderers/SW/GSRendererSW.cpp

@@ -1393,7 +1393,7 @@ bool GSRendererSW::GetScanlineGlobalData(SharedData* data)
 				gd.sel.pabe = 1;
 			}
 
-			if (PRIM->AA1 && (primclass == GS_LINE_CLASS || primclass == GS_TRIANGLE_CLASS))
+			if (IsCoverageAlpha())
 			{
 				gd.sel.aa1 = 1;
 			}
@@ -1523,6 +1523,11 @@ bool GSRendererSW::GetScanlineGlobalData(SharedData* data)
 	return true;
 }
 
+bool GSRendererSW::IsCoverageAlphaSupported()
+{
+	return IsCoverageAlpha();
+}
+
 GSRendererSW::SharedData::SharedData()
 	: m_fpsm(0)
 	, m_zpsm(0)

pcsx2/GS/Renderers/SW/GSRendererSW.h

@@ -82,7 +82,7 @@ protected:
 	template <u32 primclass>
 	void RewriteVerticesIfSTOverflow();
 
-	bool IsCoverageAlphaSupported() override { return true; }
+	bool IsCoverageAlphaSupported() override;
 public:
 	GSRendererSW(int threads);
 	~GSRendererSW() override;