target/ppc: Use tcg_gen_atomic_cmpxchg_i128 for STQCX

target/ppc: Use tcg_gen_atomic_cmpxchg_i128 for STQCX

Note that the previous direct reference to reserve_val,

-   tcg_gen_ld_i64(t1, cpu_env, (ctx->le_mode
-                                ? offsetof(CPUPPCState, reserve_val2)
-                                : offsetof(CPUPPCState, reserve_val)));

was incorrect because all references should have gone through
cpu_reserve_val.  Create a cpu_reserve_val2 tcg temp to fix this.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Daniel Henrique Barboza <danielhb413@gmail.com>
Message-Id: <20221112061122.2720163-2-richard.henderson@linaro.org>