svga: try to flag surfaces for sampling, in addition to rendering
svga: try to flag surfaces for sampling, in addition to rendering

This silences some warnings when we try to sample from surfaces that were
created for drawing, such as when blitting from one of the framebuffer
surfaces.  We were already doing the opposite situation (adding a bind
flag for rendering to surfaces declared as texture sources).

Reviewed-by: Charmaine Lee <67ce69700661ea856134ddb10419a330e5f037d7@vmware.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler