radv: enable TC-compat HTILE for 16-bit depth surfaces on GFX8

radv: enable TC-compat HTILE for 16-bit depth surfaces on GFX8

The hardware only supports 32-bit depth surfaces, but we can
enable TC-compat HTILE for 16-bit depth surfaces if no Z planes
are compressed.

The main benefit is to reduce the number of depth decompression
passes. Also, we don't need to implement DB->CB copies which is
fine.

This improves Serious Sam 2017 by +4%. Talos and F12017 are also
affected but I don't see a performance difference.

This also improves the shadowmapping Vulkan demo by 10-15%
(FPS is now similar to AMDVLK).

No CTS regressions on Polaris10.

Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>