arm64: System calls handling

This patch adds support for system calls coming from 64-bit
applications. It uses the asm-generic/unistd.h definitions with the
canonical set of system calls. The private system calls are only used
for 32-bit (compat) applications as 64-bit ones can set the TLS and
flush the caches entirely from user space.

The sys_call_table is just an array defined in a C file and it contains
pointers to the syscall functions. The array is 4KB aligned to allow the
use of the ADRP instruction (longer range ADR) in entry.S.

Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Acked-by: Nicolas Pitre <nico@linaro.org>
Acked-by: Olof Johansson <olof@lixom.net>
Acked-by: Santosh Shilimkar <santosh.shilimkar@ti.com>

arch/arm64/include/asm/unistd.h

@@ -0,0 +1,27 @@
+/*
+ * Copyright (C) 2012 ARM Ltd.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+#if !defined(__ASM_UNISTD_H) || defined(__SYSCALL)
+#define __ASM_UNISTD_H
+
+#ifndef __SYSCALL_COMPAT
+#include <asm-generic/unistd.h>
+#endif
+
+#if defined(__KERNEL__) && defined(CONFIG_COMPAT)
+#include <asm/unistd32.h>
+#endif
+
+#endif /* __ASM_UNISTD_H */