agx: Implement some shader-db stats

Instructions, bytes, and registers -- this should hold us over until we
can reverse the underlying uarch and get proper cycle estimations.

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/16268>

src/asahi/compiler/agx_compiler.h

@@ -661,6 +661,8 @@ void agx_dce(agx_context *ctx);
 void agx_ra(agx_context *ctx);
 void agx_pack_binary(agx_context *ctx, struct util_dynarray *emission);
 
+unsigned agx_write_registers(agx_instr *I, unsigned d);
+
 void agx_compute_liveness(agx_context *ctx);
 void agx_liveness_ins_update(BITSET_WORD *live, agx_instr *I);