target/unicore32: Use env_cpu, env_archcpu

Cleanup in the boilerplate that each target must define.
Replace uc32_env_get_cpu with env_archcpu.  The combination
CPU(uc32_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/unicore32/ucf64_helper.c

@@ -78,7 +78,7 @@ static inline int ucf64_exceptbits_to_host(int target_bits)
 
 void HELPER(ucf64_set_fpscr)(CPUUniCore32State *env, uint32_t val)
 {
-    UniCore32CPU *cpu = uc32_env_get_cpu(env);
+    UniCore32CPU *cpu = env_archcpu(env);
     int i;
     uint32_t changed;