i915: Fix NPOT compressed textures on 915.
i915: Fix NPOT compressed textures on 915.

We were failing at rounding, misplacing the non-baselevels.  Fixes:
3DFX_texture_compression_FXT1/fbo-generate-mipmaps
ARB_texture_compression/fbo-generate-mipmaps
EXT_texture_compression_s3tc/fbo-generate-mipmaps

Reviewed-by: Ian Romanick <2b237cafb16dc45038e85df6c85e74e6d899eba9@intel.com>

zeux/glsl-optimizer,benaadams/glsl-optimizer,mapbox/glsl-optimizer,benaadams/glsl-optimizer,benaadams/glsl-optimizer,dellis1972/glsl-optimizer,djreep81/glsl-optimizer,KTXSoftware/glsl2agal,tokyovigilante/glsl-optimizer,zz85/glsl-optimizer,zz85/glsl-optimizer,KTXSoftware/glsl2agal,tokyovigilante/glsl-optimizer,mapbox/glsl-optimizer,zeux/glsl-optimizer,adobe/glsl2agal,wolf96/glsl-optimizer,benaadams/glsl-optimizer,KTXSoftware/glsl2agal,tokyovigilante/glsl-optimizer,metora/MesaGLSLCompiler,zeux/glsl-optimizer,dellis1972/glsl-optimizer,zz85/glsl-optimizer,adobe/glsl2agal,KTXSoftware/glsl2agal,mcanthony/glsl-optimizer,benaadams/glsl-optimizer,benaadams/glsl-optimizer,dellis1972/glsl-optimizer,adobe/glsl2agal,djreep81/glsl-optimizer,zz85/glsl-optimizer,metora/MesaGLSLCompiler,KTXSoftware/glsl2agal,adobe/glsl2agal,mapbox/glsl-optimizer,metora/MesaGLSLCompiler,wolf96/glsl-optimizer,mapbox/glsl-optimizer,bkaradzic/glsl-optimizer,tokyovigilante/glsl-optimizer,bkaradzic/glsl-optimizer,dellis1972/glsl-optimizer,bkaradzic/glsl-optimizer,jbarczak/glsl-optimizer,mapbox/glsl-optimizer,wolf96/glsl-optimizer,jbarczak/glsl-optimizer,djreep81/glsl-optimizer,zz85/glsl-optimizer,tokyovigilante/glsl-optimizer,dellis1972/glsl-optimizer,jbarczak/glsl-optimizer,zz85/glsl-optimizer,adobe/glsl2agal,mcanthony/glsl-optimizer,zeux/glsl-optimizer,wolf96/glsl-optimizer,mcanthony/glsl-optimizer,bkaradzic/glsl-optimizer,zeux/glsl-optimizer,djreep81/glsl-optimizer,jbarczak/glsl-optimizer,jbarczak/glsl-optimizer,mcanthony/glsl-optimizer,djreep81/glsl-optimizer,bkaradzic/glsl-optimizer,wolf96/glsl-optimizer,mcanthony/glsl-optimizer