nir: Move shared_memory_explicit_layout bit into common shader_info

Move it out of the "cs" sub-struct, since the bit can be used for
other shader stages in the future.

This also removes a subtle issue in spirv_to_nir:
info.cs.shared_memory_explicit_layout was used without checking for
the CS shader stage.  It ended up being "harmless" since the effects
also depended on presence of shared variables.

Fixes: 5de6c5973a ("spirv: Implement SPV_KHR_workgroup_memory_explicit_layout")
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/10529>

src/amd/vulkan/radv_shader.c

@@ -645,7 +645,7 @@ radv_shader_compile_to_nir(struct radv_device *device, struct vk_shader_module *
 
    /* Lower deref operations for compute shared memory. */
    if (nir->info.stage == MESA_SHADER_COMPUTE) {
-      if (!nir->info.cs.shared_memory_explicit_layout) {
+      if (!nir->info.shared_memory_explicit_layout) {
          NIR_PASS_V(nir, nir_lower_vars_to_explicit_types, nir_var_mem_shared, shared_var_info);
       }
       NIR_PASS_V(nir, nir_lower_explicit_io, nir_var_mem_shared, nir_address_format_32bit_offset);