cpu: Replace ENV_GET_CPU with env_cpu

Now that we have both ArchCPU and CPUArchState, we can define
this generically instead of via macro in each target's cpu.h.

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

target/alpha/cpu.h

@@ -283,8 +283,6 @@ static inline AlphaCPU *alpha_env_get_cpu(CPUAlphaState *env)
     return container_of(env, AlphaCPU, env);
 }
 
-#define ENV_GET_CPU(e) CPU(alpha_env_get_cpu(e))
-
 #define ENV_OFFSET offsetof(AlphaCPU, env)
 
 #ifndef CONFIG_USER_ONLY