nir,agx: add depth=never workaround

There seems to be a hardware issue where fragment shaders with side effects get
skipped if depth testing with NEVER. Add a workaround for this case where we
discard programmatically instead.

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Acked-by: Faith Ekstrand <faith.ekstrand@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/29179>

src/compiler/nir/nir_intrinsics.py

@@ -1980,6 +1980,10 @@ system_value("sample_positions_agx", 1, bit_sizes=[32])
 # responsible for Z/S testing after its final discard. ~0/0 boolean.
 system_value("shader_part_tests_zs_agx", 1, bit_sizes=[16])
 
+# Returns whether the API depth test is NEVER. We emulate this in shader when
+# fragment side effects are used to ensure the fragment shader executes.
+system_value("depth_never_agx", 1, bit_sizes=[16])
+
 # In a fragment shader, returns the log2 of the number of samples in the
 # tilebuffer. This is the unprocessed value written in the corresponding USC
 # word. Used to determine whether sample mask writes have any effect when sample