Alpha: define syscall_get_arch()

Since Alpha supports syscall audit it now needs to have a syscall.h
which implements syscall_get_arch() rather than hard coding this value
into audit_syscall_entry().
Based-on-patch-by: Richard Briggs <rgb@redhat.com>
Signed-off-by: Eric Paris <eparis@redhat.com>
Cc: linux-alpha@vger.kernel.org

arch/alpha/include/asm/syscall.h

+#ifndef _ASM_ALPHA_SYSCALL_H
+#define _ASM_ALPHA_SYSCALL_H
+
+#include <uapi/linux/audit.h>
+
+static inline int syscall_get_arch(void)
+{
+	return AUDIT_ARCH_ALPHA;
+}
+
+#endif	/* _ASM_ALPHA_SYSCALL_H */