target/i386: Use env_cpu, env_archcpu

Cleanup in the boilerplate that each target must define.
Replace x86_env_get_cpu with env_archcpu.  The combination
CPU(x86_env_get_cpu) should have used ENV_GET_CPU to begin;
use env_cpu now.

Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

bsd-user/main.c

@@ -140,8 +140,7 @@ static void set_idt(int n, unsigned int dpl)
 
 void cpu_loop(CPUX86State *env)
 {
-    X86CPU *cpu = x86_env_get_cpu(env);
-    CPUState *cs = CPU(cpu);
+    CPUState *cs = env_cpu(env);
     int trapnr;
     abi_ulong pc;
     //target_siginfo_t info;