radeonsi: fix piglit image coherency test when use aco

spec@arb_shader_image_load_store@coherency will write to coherent image in tess shader and read it in fragmant shader. There is a geometry shader in between.

When lower ngg for the geometry shader, it will wait memory writes before pos0 export if there's no param output to prevent fragment shader start early and read any previous memory writes.

We need to update the memory writes info of GS with ES ones because ES and GS is merged into one shader but when nir they are separated. LLVM does not have this problem because it will add memory write wait at the beginning of GS automatically.