iris: Fix fast-clearing of depth via glClearTex(Sub)Image
If we clear depth only texture via glClearTex(Sub)Image it may cause: ../src/intel/blorp/blorp_genX_exec.h:1554: blorp_emit_surface_states: Assertion `params->depth.enabled || params->stencil.enabled' failed. due to clear_depth_stencil calling blorp_clear_depth_stencil when depth is already fast-cleared and there is no stencil. Fixes piglit test: arb_clear_texture-depth Fixes: 51638cf1 Signed-off-by:Danylo Piliaiev <danylo.piliaiev@globallogic.com> Reviewed-by:
Lionel Landwerlin <lionel.g.landwerlin@intel.com> Part-of: <mesa/mesa!5770> (cherry picked from commit 77844690)