llvmpipe/blit: for 32-bit unorm depth blits just copy 32-bit

Don't have the shader do a 32-bit unorn to float conversion,
the values don't remain accurate then.

Fixes:
GTF-GL45.gtf30.GL3Tests.framebuffer_blit.framebuffer_blit_functionality_multisampled_to_singlesampled_blit
for 32-bit unorm depth buffers.

Cc: "20.2" <mesa-stable@lists.freedesktop.org>
Reviewed-by: Roland Scheidegger <sroland@vmware.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6044>
1 file changed