x86/entry: Convert Alignment check exception to IDTENTRY

Convert #AC to IDTENTRY_ERRORCODE:
  - Implement the C entry point with DEFINE_IDTENTRY
  - Emit the ASM stub with DECLARE_IDTENTRY
  - Remove the ASM idtentry in 64bit
  - Remove the open coded ASM entry code in 32bit
  - Fixup the XEN/PV code
  - Remove the old prototypes
  - Remove the RCU warning as the new entry macro ensures correctness

No functional change.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Acked-by: Andy Lutomirski <luto@kernel.org>
Link: https://lkml.kernel.org/r/20200505134905.928967113@linutronix.de

arch/x86/kernel/traps.c

@@ -270,12 +270,10 @@ DEFINE_IDTENTRY_ERRORCODE(exc_stack_segment)
 		      0, NULL);
 }
 
-dotraplinkage void do_alignment_check(struct pt_regs *regs, long error_code)
+DEFINE_IDTENTRY_ERRORCODE(exc_alignment_check)
 {
 	char *str = "alignment check";
 
-	RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU");
-
 	if (notify_die(DIE_TRAP, str, regs, error_code, X86_TRAP_AC, SIGBUS) == NOTIFY_STOP)
 		return;