radv: implement fast HTILE clears for depth or stencil only on GFX9

radv: implement fast HTILE clears for depth or stencil only on GFX9

This allows to fast clear the depth part (or the stencil part)
of a depth+stencil surface when HTILE is enabled. I didn't test
on GFX8, so it's disabled currently.

This gives a very nice boost, for example when clearing the depth
aspect of a 4096x4096 D32_SFLOAT_S8_UINT image (18x faster).

BEFORE: 235 us
AFTER: 13 us

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