linux-user: move ppc/ppc64 signal.c parts to ppc directory

No code change, only move code from signal.c to
ppc/signal.c, except adding includes and
exporting setup_frame() and setup_rt_frame().

Signed-off-by: Laurent Vivier <laurent@vivier.eu>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20180424192635.6027-20-laurent@vivier.eu>

linux-user/ppc/target_signal.h

@@ -26,5 +26,11 @@ static inline abi_ulong get_sp_from_cpustate(CPUPPCState *state)
     return state->gpr[1];
 }
 
-
+#if !defined(TARGET_PPC64)
+void setup_frame(int sig, struct target_sigaction *ka,
+                 target_sigset_t *set, CPUPPCState *env);
+#endif
+void setup_rt_frame(int sig, struct target_sigaction *ka,
+                    target_siginfo_t *info,
+                    target_sigset_t *set, CPUPPCState *env);
 #endif /* PPC_TARGET_SIGNAL_H */