r600g: Make unaligned 3D textures work on +evergreen
r600g: Make unaligned 3D textures work on +evergreen

The layersize calculation is slightly different on +evergreen.
This makes mpeg2 video decoding and piglits texture-packed-formats
test work correctly on this hardware.

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