vc4: Enable nir_lower_io for uniforms

Altough the driver isn't expected to receive nir_var_uniform types
from GLSL this happens currently for one of the internal driver shaders.

At vc4_get_yuv_fs at vc4_blit.c there is a "stride" nir_var_uniform
variable that needs to be lowered so the shader can be compiled.

This regression was affecting several piglit tests under
spec/ext_image_dma_buf_import and at least MythTV application.

Fixes: 96d99f2ecc ("vc4: Only call nir_lower_io on shader_in/out")
Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/3536
Reviewed-by: Eric Anholt <eric@anholt.net>
Tested-by: Piotr Oniszczuk <piotr.oniszczuk@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7160>

src/gallium/drivers/vc4/vc4_program.c

@@ -2474,7 +2474,8 @@ vc4_shader_state_create(struct pipe_context *pctx,
         if (s->info.stage == MESA_SHADER_VERTEX)
                 NIR_PASS_V(s, nir_lower_point_size, 1.0f, 0.0f);
 
-        NIR_PASS_V(s, nir_lower_io, nir_var_shader_in | nir_var_shader_out,
+        NIR_PASS_V(s, nir_lower_io,
+                   nir_var_shader_in | nir_var_shader_out | nir_var_uniform,
                    type_size, (nir_lower_io_options)0);
 
         NIR_PASS_V(s, nir_lower_regs_to_ssa);