linux-user: create target_structs header to place ipc_perm and shmid_ds

Creating target_structs header in linux-user/$arch/ and making
target_ipc_perm and target_shmid_ds its first inhabitants.
The struct defintions may/should be further fine-tuned by arch maintainers.

Signed-off-by: Petar Jovanovic <petar.jovanovic@imgtec.com>
Signed-off-by: Riku Voipio <riku.voipio@linaro.org>
(cherry picked from commit 55a2b1631f)

Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>

linux-user/qemu.h

@@ -452,5 +452,6 @@ static inline void *lock_user_string(abi_ulong guest_addr)
  */
 #include "target_cpu.h"
 #include "target_signal.h"
+#include "target_structs.h"
 
 #endif /* QEMU_H */