radeonsi: fix small primitive culling with MSAA force-disabled and smoothing

radeonsi: fix small primitive culling with MSAA force-disabled and smoothing

The problem was that the shader constants were based on the framebuffer
sample count and ignored the multisample enable state and the line/polygon
smoothing state, which uses MSAA rasterization that only sets SampleMaskIn
to get the coverage for alpha-blended smoothing (the PS epilog computes
the alpha channel from SampleMaskIn and blending generates the AA results).

- This is a complete rework that adds a new state for NGG cull constants.
- It fixes the same thing for the prim discard compute shader.
- It documents how VS_STATE.SMALL_PRIM_PRECISION is encoded.

It fixes blue corruption in Unigine Heaven with MSAA and Medium details
or better.

Fixes: 7648060dc03 - radeonsi: enable NGG culling by default on gfx10.3 dGPUs

Acked-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/8022>