xtensa: clean up syscall.h

Drop non-existent/unneeded function declarations, add header guard.
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>

arch/xtensa/include/asm/syscall.h

 /*
- * include/asm-xtensa/syscall.h
- *
  * This file is subject to the terms and conditions of the GNU General Public
  * License.  See the file "COPYING" in the main directory of this archive
  * for more details.
  *
  * Copyright (C) 2001 - 2007 Tensilica Inc.
+ * Copyright (C) 2018 Cadence Design Systems Inc.
  */
 
+#ifndef _ASM_SYSCALL_H
+#define _ASM_SYSCALL_H
+
 struct pt_regs;
-asmlinkage long xtensa_ptrace(long, long, long, long);
-asmlinkage long xtensa_sigreturn(struct pt_regs*);
+
 asmlinkage long xtensa_rt_sigreturn(struct pt_regs*);
 asmlinkage long xtensa_shmat(int, char __user *, int);
 asmlinkage long xtensa_fadvise64_64(int, int,
 				    unsigned long long, unsigned long long);
 
-/* Should probably move to linux/syscalls.h */
-struct pollfd;
-asmlinkage long sys_pselect6(int n, fd_set __user *inp, fd_set __user *outp,
-			     fd_set __user *exp, struct timespec __user *tsp,
-			     void __user *sig);
-asmlinkage long sys_ppoll(struct pollfd __user *ufds, unsigned int nfds,
-			  struct timespec __user *tsp,
-			  const sigset_t __user *sigmask,
-			  size_t sigsetsize);
+#endif