radv: Disable shader disassembly when no disassembler is available

ACO relies on LLVM to disassemble AMD shaders for ISAs newer than GFX7,
so disassembly needs to be skipped when LLVM is not enabled.

For vkGetPipelineExecutableInternalRepresentationsKHR and vkGetShaderInfoAMD,
the disassembly will not be reported anymore if it can't be generated.

Reviewed-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/11319>

src/amd/vulkan/radv_pipeline.c

@@ -6095,7 +6095,7 @@ radv_GetPipelineExecutableInternalRepresentationsKHR(
    ++p;
 
    /* Disassembler */
-   if (p < end) {
+   if (p < end && shader->disasm_string) {
       p->isText = true;
       desc_copy(p->name, "Assembly");
       desc_copy(p->description, "Final Assembly");