[DG2] iris, anv: Failures when sampling HiZ_CCS after resolve

This issue is for debugging and discussing an unknown issue observed with HiZ_CCS and sampling. @tpalli documented a set of piglit tests that fail on DG2 when HIZ is enabled with CCS. Some of these include:

    piglit.spec.!opengl 1_1.depthstencil-default_fb-copypixels.dg2m64
    piglit.spec.arb_depth_buffer_float.fbo-depth-gl_depth_component32f-blit.dg2m64
    piglit.spec.arb_depth_texture.fbo-depth-gl_depth_component32-blit.dg2m64
    piglit.spec.arb_texture_cube_map.copyteximage cube samples=8.dg2m64
    piglit.spec.ext_framebuffer_multisample.unaligned-blit 2 depth msaa.dg2m64
    piglit.spec.ext_framebuffer_multisample.accuracy 4 depth_resolve small depthstencil.dg2m64
    piglit.spec.ext_packed_depth_stencil.fbo-depthstencil-gl_depth24_stencil8-copypixels.dg2m64
    piglit.spec.ext_texture_array.copyteximage 1d_array samples=6.dg2m64
    piglit.spec.ext_texture_array.copyteximage 2d_array samples=16.dg2m64

We've found the following things to help:

1. Doing a DC flush after HiZ resolves: !22717 (merged)
2. Keeping compression enabled in the sampler: nchery/mesa@a1c80af4
3. ?

/cc @tpalli @llandwerlin @kwg