anv: implement VK_KHR_separate_depth_stencil_layouts

anv: implement VK_KHR_separate_depth_stencil_layouts

v2: Use ternary to simplify code (Jason)

v3: Reorder switch cases to follow existing section ordering (Nanley)
    Add missing comment in cmd_buffer_end_subpass() about new layout (Nanley)

v4: Fix layout comparison for stencil case (Nanley)
    Update a few more comments (Nanley)
    Move VK_IMAGE_LAYOUT_STENCIL_ATTACHMENT_OPTIMAL_KHR in color
    attachment case for future stencil-CCS support (Nanley)

v5: Missed comments update (Nanley)
    Updated relnotes.txt (Lionel)

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Reviewed-by: Nanley Chery <nanley.g.chery@intel.com>