platformsupport/scenes/opengl: fix simpledrm

With simpledrm, only linear modifiers are supported, but with llvmpipe, only
implicit modifiers are supported. As it's still possible to allocate linear
buffers without modififer support by using GBM_BO_USE_LINEAR, this commit fixes
that problem by adding linear modififers to the supported list.

src/platformsupport/scenes/opengl/egldisplay.cpp

@@ -289,7 +289,7 @@ QHash<uint32_t, QList<uint64_t>> EglDisplay::queryImportFormats(Filter filter) c
             }
         }
         if (filter != Filter::ExternalOnly) {
-            ret.insert(format, {DRM_FORMAT_MOD_INVALID});
+            ret.insert(format, {DRM_FORMAT_MOD_INVALID, DRM_FORMAT_MOD_LINEAR});
         }
     }
     return ret;