pan/mdg: Do per-sample framebuffer loads

EXT_shader_framebuffer_fetch requires the fetched value to be per-sample, so we
need to load the sample id when in a fragment shader.

Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5930>

src/compiler/nir/nir_intrinsics.py

@@ -866,7 +866,7 @@ intrinsic("bindless_resource_ir3", [1], dest_comp=1, indices=[DESC_SET], flags=[
 # src[] = { value }
 store("raw_output_pan", [], [])
 store("combined_output_pan", [1, 1, 1], [BASE, COMPONENT])
-load("raw_output_pan", [], [BASE], [CAN_ELIMINATE, CAN_REORDER])
+load("raw_output_pan", [1], [BASE], [CAN_ELIMINATE, CAN_REORDER])
 
 # Loads the sampler paramaters <min_lod, max_lod, lod_bias>
 # src[] = { sampler_index }