i965/miptree: Support depth in get_isl_clear_color
i965/miptree: Support depth in get_isl_clear_color

Reviewed-by: Topi Pohjolainen <749697f19798b7f640b17221fd283b903825f071@intel.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler