mesa/st: Don't use 4bits for GL_UNSIGNED_BYTE_3_3_2(_REV)
mesa/st: Don't use 4bits for GL_UNSIGNED_BYTE_3_3_2(_REV)

4bits and 3bits quantitization values differ significantly for
values other than 0 and 1.

Fixes piglit draw-pixels for softpipe/llvmpipe.

NOTE: Probably a candidate for stable branches.

Reviewed-by: Brian Paul <3cb4e1df5ec4da2c7c4af7c52cec8cf340a55a10@vmware.com>
Reviewed-by: Marek Olšák <74bac9a67a04041c3586cda013cc5a11352e67be@gmail.com>

zz85/glsl-optimizer,bkaradzic/glsl-optimizer,zz85/glsl-optimizer,tokyovigilante/glsl-optimizer,djreep81/glsl-optimizer,djreep81/glsl-optimizer,mcanthony/glsl-optimizer,benaadams/glsl-optimizer,jbarczak/glsl-optimizer,zz85/glsl-optimizer,bkaradzic/glsl-optimizer,benaadams/glsl-optimizer,dellis1972/glsl-optimizer,wolf96/glsl-optimizer,mcanthony/glsl-optimizer,zz85/glsl-optimizer,wolf96/glsl-optimizer,zeux/glsl-optimizer,djreep81/glsl-optimizer,zz85/glsl-optimizer,metora/MesaGLSLCompiler,bkaradzic/glsl-optimizer,dellis1972/glsl-optimizer,zz85/glsl-optimizer,djreep81/glsl-optimizer,jbarczak/glsl-optimizer,mapbox/glsl-optimizer,mcanthony/glsl-optimizer,jbarczak/glsl-optimizer,zeux/glsl-optimizer,dellis1972/glsl-optimizer,wolf96/glsl-optimizer,tokyovigilante/glsl-optimizer,metora/MesaGLSLCompiler,benaadams/glsl-optimizer,tokyovigilante/glsl-optimizer,dellis1972/glsl-optimizer,zeux/glsl-optimizer,benaadams/glsl-optimizer,benaadams/glsl-optimizer,mapbox/glsl-optimizer,benaadams/glsl-optimizer,mapbox/glsl-optimizer,mapbox/glsl-optimizer,zeux/glsl-optimizer,bkaradzic/glsl-optimizer,mcanthony/glsl-optimizer,tokyovigilante/glsl-optimizer,mapbox/glsl-optimizer,jbarczak/glsl-optimizer,mcanthony/glsl-optimizer,bkaradzic/glsl-optimizer,tokyovigilante/glsl-optimizer,wolf96/glsl-optimizer,jbarczak/glsl-optimizer,metora/MesaGLSLCompiler,dellis1972/glsl-optimizer,wolf96/glsl-optimizer,djreep81/glsl-optimizer,zeux/glsl-optimizer