freedreno/a6xx: Support some depth/stencil blits on blitter

freedreno/a6xx: Support some depth/stencil blits on blitter

We can rewrite almost all depth stencil blits to various red-only
blits.  The exception is depth-only or stencil-only blits into z24s8
combined depth stencil buffer. We can fall back for depth-only, but
stencil-only remains broken.

Fixes

  dEQP-GLES3.functional.fbo.blit.depth_stencil.depth24_stencil8_basic
  dEQP-GLES3.functional.fbo.blit.depth_stencil.depth24_stencil8_scale
  dEQP-GLES3.functional.fbo.blit.depth_stencil.depth32f_stencil8_basic
  dEQP-GLES3.functional.fbo.blit.depth_stencil.depth32f_stencil8_scale
  dEQP-GLES3.functional.fbo.blit.depth_stencil.depth32f_stencil8_stencil_only

Reviewed-by: Rob Clark <robdclark@gmail.com>
Signed-off-by: Kristian H. Kristensen <hoegsberg@chromium.org>