vrend: Reset shader_dirty and cs_shader_dirty when emitted

This results in reemitting the shaders over and over which causes a performance hit.

Benchmarks using glbench:

Before: @RESULT: fbofill_tex_bilinear_32                       = 942.40 mpixels_sec @RESULT: fbofill_tex_bilinear_64                       = 3736.99 mpixels_sec

After: @RESULT: fbofill_tex_bilinear_32 = 1124.72 mpixels_sec @RESULT: fbofill_tex_bilinear_64 = 4222.07 mpixels_sec

Signed-off-by: Stéphane Marchesin marcheu@chromium.org