ipc: add semget syscall wrapper

Provide ksys_semget() wrapper to avoid in-kernel calls to this syscall.
The ksys_ prefix denotes that this function is meant as a drop-in
replacement for the syscall. In particular, it uses the same calling
convention as sys_semget().

This patch is part of a series which removes in-kernel calls to syscalls.
On this basis, the syscall entry path can be streamlined. For details, see
http://lkml.kernel.org/r/[email protected]

Cc: Al Viro <[email protected]>
Cc: Andrew Morton <[email protected]>
Signed-off-by: Dominik Brodowski <[email protected]>

ipc/util.h

@@ -240,6 +240,7 @@ static inline int compat_ipc_parse_version(int *cmd)
 long ksys_semtimedop(int semid, struct sembuf __user *tsops,
 		     unsigned int nsops,
 		     const struct timespec __user *timeout);
+long ksys_semget(key_t key, int nsems, int semflg);
 
 /* for CONFIG_ARCH_WANT_OLD_COMPAT_IPC */
 #ifdef CONFIG_COMPAT