Detect softpipe and llvmpipe on Mesa 20.2+

It seems like the vendor string changed from "VMware Inc." to "Mesa/X.org".

autotests/libkwineffects/data/glplatform/llvmpipe-10.0

@@ -0,0 +1,22 @@
+[Driver]
+Vendor=Mesa/X.org
+Renderer=llvmpipe (LLVM 10.0.1, 256 bits)
+Version=3.1 Mesa 20.2.1
+ShadingLanguageVersion=1.40
+
+[Settings]
+LooseBinding=true
+GLSL=true
+TextureNPOT=true
+Mesa=true
+Gallium=true
+SoftwareEmulation=true
+GLVersion=3,1
+GLSLVersion=1,40
+MesaVersion=20,2,1
+GalliumVersion=0,4
+DriverVersion=20,2,1
+Driver=12
+ChipClass=99999
+Compositor=9
+

libkwineffects/kwinglplatform.cpp

@@ -894,12 +894,12 @@ void GLPlatform::detect(OpenGLPlatformInterface platformInterface)
         }
 
         // softpipe
-        else if (m_vendor == "VMware, Inc." && m_chipset == "softpipe" ) {
+        else if (m_chipset == "softpipe") {
             m_driver = Driver_Softpipe;
         }
 
         // llvmpipe
-        else if (m_vendor == "VMware, Inc." && m_chipset == "llvmpipe") {
+        else if (m_chipset == "llvmpipe") {
             m_driver = Driver_Llvmpipe;
         }