x86/entry: Convert XEN hypercall vector to IDTENTRY_SYSVEC

Convert the last oldstyle defined vector to IDTENTRY_SYSVEC:

  - Implement the C entry point with DEFINE_IDTENTRY_SYSVEC
  - Emit the ASM stub with DECLARE_IDTENTRY_SYSVEC
  - Remove the ASM idtentries in 64-bit
  - Remove the BUILD_INTERRUPT entries in 32-bit
  - Remove the old prototypes

Fixup the related XEN code by providing the primary C entry point in x86 to
avoid cluttering the generic code with X86'isms.

No functional change.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Andy Lutomirski <luto@kernel.org>
Link: https://lore.kernel.org/r/20200521202119.741950104@linutronix.de

drivers/xen/events/events_base.c

@@ -37,6 +37,7 @@
 #ifdef CONFIG_X86
 #include <asm/desc.h>
 #include <asm/ptrace.h>
+#include <asm/idtentry.h>
 #include <asm/irq.h>
 #include <asm/io_apic.h>
 #include <asm/i8259.h>
@@ -1236,9 +1237,6 @@ void xen_evtchn_do_upcall(struct pt_regs *regs)
 	struct pt_regs *old_regs = set_irq_regs(regs);
 
 	irq_enter();
-#ifdef CONFIG_X86
-	inc_irq_stat(irq_hv_callback_count);
-#endif
 
 	__xen_evtchn_do_upcall();
 
@@ -1658,7 +1656,7 @@ static __init void xen_alloc_callback_vector(void)
 		return;
 
 	pr_info("Xen HVM callback vector for event delivery is enabled\n");
-	alloc_intr_gate(HYPERVISOR_CALLBACK_VECTOR, xen_hvm_callback_vector);
+	alloc_intr_gate(HYPERVISOR_CALLBACK_VECTOR, asm_sysvec_xen_hvm_callback);
 }
 #else
 void xen_setup_callback_vector(void) {}