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/xen/enlighten_pv.c

@@ -633,7 +633,7 @@ static struct trap_array_entry trap_array[] = {
 	TRAP_ENTRY(exc_general_protection,		false ),
 	TRAP_ENTRY(exc_spurious_interrupt_bug,		false ),
 	TRAP_ENTRY(exc_coprocessor_error,		false ),
-	{ alignment_check,             xen_alignment_check,             false },
+	TRAP_ENTRY(exc_alignment_check,			false ),
 	{ simd_coprocessor_error,      xen_simd_coprocessor_error,      false },
 };
 

arch/x86/xen/xen-asm_64.S

@@ -46,7 +46,7 @@ xen_pv_trap asm_exc_general_protection
 xen_pv_trap page_fault
 xen_pv_trap asm_exc_spurious_interrupt_bug
 xen_pv_trap asm_exc_coprocessor_error
-xen_pv_trap alignment_check
+xen_pv_trap asm_exc_alignment_check
 #ifdef CONFIG_X86_MCE
 xen_pv_trap machine_check
 #endif /* CONFIG_X86_MCE */