st/mesa: Record samplers for extra planes in info->textures_used.

Normally gl_nir_lower_samplers_as_deref records info->textures_used
for us, but this pass runs after that, attempting to assign samplers
in the same order as st_atom_texture's external_samplers_used loop
so the stars align and we get the same locations.

Since we're adding textures late, we need to amend info->textures_used.

iris uses info->textures_used to set up texture bindings; this fixes
Piglit's ext_image_dma_buf_import-sample-{nv12,yuv420,yvu420} there.

Reviewed-by: Rob Clark <robdclark@gmail.com>

src/mesa/state_tracker/st_nir_lower_tex_src_plane.c

@@ -33,6 +33,8 @@
 #include "st_nir.h"
 
 typedef struct {
+   struct shader_info *info;
+
    unsigned lower_2plane;
    unsigned lower_3plane;
 
@@ -85,6 +87,8 @@ lower_tex_src_plane_block(lower_tex_src_state *state, nir_block *block)
 
          tex->texture_index = tex->sampler_index =
                state->sampler_map[y_samp][plane[0].i32 - 1];
+
+         state->info->textures_used |= 1u << tex->texture_index;
       }
 
       nir_tex_instr_remove_src(tex, plane_index);
@@ -108,6 +112,7 @@ st_nir_lower_tex_src_plane(struct nir_shader *shader, unsigned free_slots,
 {
    lower_tex_src_state state = {0};
 
+   state.info = &shader->info;
    state.lower_2plane = lower_2plane;
    state.lower_3plane = lower_3plane;