x86,64: Separate arg1 from rbp handling in SAVE_REGS_IRQ

Just for clarity in the code. Have a first block that handles
the frame pointer and a separate one that handles pt_regs
pointer and its use.
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jan Beulich <JBeulich@novell.com>

arch/x86/kernel/entry_64.S

@@ -310,9 +310,10 @@ ENDPROC(native_usergs_sysret64)
 	movq_cfi r10, R10-RBP
 	movq_cfi r11, R11-RBP
 
-	leaq -RBP(%rsp),%rdi	/* arg1 for handler */
 	movq_cfi rbp, 0		/* push %rbp */
 	movq %rsp, %rbp
+
+	leaq -RBP(%rsp),%rdi	/* arg1 for handler */
 	testl $3, CS(%rdi)
 	je 1f
 	SWAPGS