nir: Add missing dependency on nir_opcodes.py

Commit 38800b38 changed nir_opcodes.py, but that doesn't seem to have
triggered nir_opt_algebraic.py.  The change in 75ef5991 depends on
opt_algebraic lowering 16-bit versions of slt, but if opt_algebraic is
not rebuilt, this may not happen.  This resulted in some people seeing
assertion failures in, for example,
dEQP-VK.spirv_assembly.instruction.compute.float16.arithmetic_3.step,
due to the backend seeing nir_op_slt that it didn't know how to handle.

v2: Add nir_opcodes.py to nir_algebraic_py so that all the per-driver
algebraic passes pick up the dependency too.  Rename it to
nir_algebraic_depends.  Suggested by Emma.

Closes: #6047
Fixes: d1992255bb ("meson: Add build Intel "anv" vulkan driver")
Reviewed-by: Emma Anholt <emma@anholt.net>
Acked-by: Dave Airlie <airlied@redhat.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/15050>

src/intel/compiler/meson.build

@@ -148,7 +148,7 @@ brw_nir_trig = custom_target(
     prog_python, '@INPUT@',
     '-p', join_paths(meson.source_root(), 'src/compiler/nir/'),
   ],
-  depend_files : nir_algebraic_py,
+  depend_files : nir_algebraic_depends,
   capture : true,
 )