amd: change chip_class naming to "enum amd_gfx_level gfx_level"

This aligns the naming with PAL.

Acked-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Acked-by: Pierre-Eric Pellou-Prayer <pierre-eric.pelloux-prayer@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/16469>

src/amd/compiler/aco_optimizer_postRA.cpp

@@ -194,7 +194,7 @@ try_apply_branch_vcc(pr_opt_ctx& ctx, aco_ptr<Instruction>& instr)
     */
 
    /* Don't try to optimize this on GFX6-7 because SMEM may corrupt the vccz bit. */
-   if (ctx.program->chip_class < GFX8)
+   if (ctx.program->gfx_level < GFX8)
       return;
 
    if (instr->format != Format::PSEUDO_BRANCH || instr->operands.size() == 0 ||