gallium/radeon: rename r600_texture_disable_cmask -> discard_cmask
gallium/radeon: rename r600_texture_disable_cmask -> discard_cmask

because it doesn't decompress

Reviewed-by: Alex Deucher <08dc22c6156113f2deff178e35e3ed9b24d6af9e@amd.com>
Reviewed-by: Nicolai Hähnle <0d0be6cf5ad662651be2dc5dfd44aa2b09d4c1cc@amd.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler