zink: workaround depth sampler border color when z24 is z32

If there is a z24 unorm depth buffer, but it's the hw is using a z32, the border color needs to be clamped appropriately.

This creates a second sampler with the clamped border color, and uses it if needed. The checks might need some tightening up.

Fixes: zink on radv dEQP-GLES31.functional.texture.border_clamp.range_clamp.nearest_unorm_depth