x86/entry: Convert double fault exception to IDTENTRY_DF

Convert #DF to IDTENTRY_DF
  - Implement the C entry point with DEFINE_IDTENTRY_DF
  - Emit the ASM stub with DECLARE_IDTENTRY_DF on 64bit
  - Remove the ASM idtentry in 64bit
  - Adjust the 32bit shim code
  - Fixup the XEN/PV code
  - Remove the old prototypes

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/20200505135315.583415264@linutronix.de

arch/x86/xen/enlighten_pv.c

@@ -616,7 +616,7 @@ struct trap_array_entry {
 
 static struct trap_array_entry trap_array[] = {
 	TRAP_ENTRY_REDIR(exc_debug, exc_xendebug,	true  ),
-	{ double_fault,                xen_double_fault,                true },
+	TRAP_ENTRY(exc_double_fault,			true  ),
 #ifdef CONFIG_X86_MCE
 	TRAP_ENTRY(exc_machine_check,			true  ),
 #endif
@@ -651,7 +651,7 @@ static bool __ref get_trap_addr(void **addr, unsigned int ist)
 	 * Replace trap handler addresses by Xen specific ones.
 	 * Check for known traps using IST and whitelist them.
 	 * The debugger ones are the only ones we care about.
-	 * Xen will handle faults like double_fault, * so we should never see
+	 * Xen will handle faults like double_fault, so we should never see
 	 * them.  Warn if there's an unexpected IST-using fault handler.
 	 */
 	for (nr = 0; nr < ARRAY_SIZE(trap_array); nr++) {