winsys/amdgpu: set flags correctly when allocating depth-stencil buffers
winsys/amdgpu: set flags correctly when allocating depth-stencil buffers

This mimics Vulkan. It also documents how to fix stencil texturing.

Reviewed-by: Michel Dänzer <242b79f0804cf52679d58f27ed754158c1323c75@amd.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler