intel/compiler: Move spill/fill tracking to the register allocator

Originally, we had virtual opcodes for scratch access, and let the
generator count spills/fills separately from other sends.  Later, we
started using the generic SHADER_OPCODE_SEND for spills/fills on some
generations of hardware, and simply detected stateless messages there.

But then we started using stateless messages for other things:
- anv uses stateless messages for the buffer device address feature.
- nir_opt_large_constants generates stateless messages.
- XeHP curbe setup can generate stateless messages.

So counting stateless messages is not accurate.  Instead, we move the
spill/fill accounting to the register allocator, as it generates such
things, as well as the load/store_scratch intrinsic handling, as those
are basically spill/fills, just at a higher level.

Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/16691>

src/intel/compiler/brw_fs.h

@@ -81,6 +81,8 @@ offset(const fs_reg &reg, const brw::fs_builder &bld, unsigned delta)
 struct shader_stats {
    const char *scheduler_mode;
    unsigned promoted_constants;
+   unsigned spill_count;
+   unsigned fill_count;
 };
 
 /**