agx: Handle fragment shader side effects

Fragment shaders with side effects need to be lowered to ensure they execute for
all shaded pixels but no helper threads. Add a lowering pass to handle this.

Fixes dEQP-GLES31.functional.shaders.opaque_type_indexing.atomic_counter.const_literal_fragment

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/21712>

src/asahi/compiler/agx_compiler.h

@@ -834,6 +834,7 @@ bool agx_nir_lower_load_mask(nir_shader *shader);
 bool agx_nir_lower_address(nir_shader *shader);
 bool agx_nir_lower_ubo(nir_shader *shader);
 bool agx_nir_lower_shared_bitsize(nir_shader *shader);
+bool agx_nir_lower_frag_sidefx(nir_shader *s);
 
 #ifdef __cplusplus
 } /* extern C */