cpu: Move cpu_index field to CPUState

Note that target-alpha accesses this field from TCG, now using a
negative offset. Therefore the field is placed last in CPUState.

Pass PowerPCCPU to [kvm]ppc_fixup_cpu() to facilitate this change.

Move common parts of mips cpu_state_reset() to mips_cpu_reset().

Acked-by: Richard Henderson <rth@twiddle.net> (for alpha)
[AF: Rebased onto ppc CPU subclasses and openpic changes]
Signed-off-by: Andreas Färber <afaerber@suse.de>

include/exec/gdbstub.h

@@ -35,7 +35,8 @@ static inline int cpu_index(CPUArchState *env)
 #if defined(CONFIG_USER_ONLY) && defined(CONFIG_USE_NPTL)
     return env->host_tid;
 #else
-    return env->cpu_index + 1;
+    CPUState *cpu = ENV_GET_CPU(env);
+    return cpu->cpu_index + 1;
 #endif
 }