glamor: Use software fb for 1bpp pixmap.
For 1bpp pixmap, software fb get better performance than GL surface. The main reason is that fbo doesn't support 1bpp texture as internal format, so we have to translate a 1bpp bitmap to a 8bit alpha format each time which is very inefficient. And the previous implementation is not supported by the latest OpenGL 4.0, the GL_BITMAP was deprecated. Signed-off-by: Zhigang Gong <email@example.com>
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