target/hppa: Use env_cpu, env_archcpu

Cleanup in the boilerplate that each target must define.
Replace hppa_env_get_cpu with env_archcpu.  The combination
CPU(hppa_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>

target/hppa/cpu.h

@@ -222,11 +222,6 @@ struct HPPACPU {
     QEMUTimer *alarm_timer;
 };
 
-static inline HPPACPU *hppa_env_get_cpu(CPUHPPAState *env)
-{
-    return container_of(env, HPPACPU, env);
-}
-
 #define ENV_OFFSET      offsetof(HPPACPU, env)
 
 typedef CPUHPPAState CPUArchState;