target/xtensa: Use env_archcpu() in update_c[compare|count]()

When CPUArchState* is available (here CPUXtensaState*), we
can use the fast env_archcpu() macro to get ArchCPU* (here
XtensaCPU*). The QOM cast XTENSA_CPU() macro will be slower
when building with --enable-qom-cast-debug.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Acked-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <20231009110239.66778-5-philmd@linaro.org>

target/xtensa/op_helper.c

@@ -37,7 +37,7 @@
 
 void HELPER(update_ccount)(CPUXtensaState *env)
 {
-    XtensaCPU *cpu = XTENSA_CPU(env_cpu(env));
+    XtensaCPU *cpu = env_archcpu(env);
     uint64_t now = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
 
     env->ccount_time = now;
@@ -58,7 +58,7 @@ void HELPER(wsr_ccount)(CPUXtensaState *env, uint32_t v)
 
 void HELPER(update_ccompare)(CPUXtensaState *env, uint32_t i)
 {
-    XtensaCPU *cpu = XTENSA_CPU(env_cpu(env));
+    XtensaCPU *cpu = env_archcpu(env);
     uint64_t dcc;
 
     qatomic_and(&env->sregs[INTSET],