audit: fix build error when asm/syscall.h does not exist

avr32 does not have an asm/syscall.h file.  We need the
syscall_get_arch() definition from that file for all arch's which
support CONFIG_AUDITSYSCALL.  Obviously avr32 is not one of those
arch's.  Move the include inside the CONFIG_AUDITSYSCALL such that we
only do the include if we need the results.

When the syscall_get_arch() call is moved inside __audit_syscall_entry()
this include can be dropped entirely.  But that is going to require some
assembly changes on x86* in a patch that is not ready for the tree...
Reported-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Eric Paris <eparis@redhat.com>

include/linux/audit.h

@@ -26,7 +26,6 @@
 #include <linux/sched.h>
 #include <linux/ptrace.h>
 #include <uapi/linux/audit.h>
-#include <asm/syscall.h>
 
 struct audit_sig_info {
 	uid_t		uid;
@@ -110,6 +109,8 @@ extern void audit_log_session_info(struct audit_buffer *ab);
 #endif
 
 #ifdef CONFIG_AUDITSYSCALL
+#include <asm/syscall.h> /* for syscall_get_arch() */
+
 /* These are defined in auditsc.c */
 				/* Public API */
 extern int  audit_alloc(struct task_struct *task);