util: fix incorrect Z bit masking in util_clear_depth_stencil()
util: fix incorrect Z bit masking in util_clear_depth_stencil()

For PIPE_FORMAT_Z24_UNORM_S8_UINT, the Z bits are in the 24
least significant bits.

Fixes http://bugs.freedesktop.org/show_bug.cgi?id=60527
and http://bugs.freedesktop.org/show_bug.cgi?id=60524
and http://bugs.freedesktop.org/show_bug.cgi?id=60047

Note: This is a candidate for the stable branches.

Reviewed-by: Jose Fonseca <61b5a29db2c0650f7c8510f93eece059c1b09320@vmware.com>

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