x86/entry/32: Fix XEN_PV build dependency

xenpv_exc_nmi() and xenpv_exc_debug() are only defined on 64-bit kernels,
but they snuck into the 32-bit build via <asm/identry.h>, causing the link
to fail:

  ld: arch/x86/entry/entry_32.o: in function `asm_xenpv_exc_nmi':
  (.entry.text+0x817): undefined reference to `xenpv_exc_nmi'

  ld: arch/x86/entry/entry_32.o: in function `asm_xenpv_exc_debug':
  (.entry.text+0x827): undefined reference to `xenpv_exc_debug'

Only use them on 64-bit kernels.

Fixes: f41f082: ("x86/entry/xen: Route #DB correctly on Xen PV")
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/include/asm/idtentry.h

@@ -553,7 +553,7 @@ DECLARE_IDTENTRY_RAW(X86_TRAP_MC,	exc_machine_check);
 
 /* NMI */
 DECLARE_IDTENTRY_NMI(X86_TRAP_NMI,	exc_nmi);
-#ifdef CONFIG_XEN_PV
+#if defined(CONFIG_XEN_PV) && defined(CONFIG_X86_64)
 DECLARE_IDTENTRY_RAW(X86_TRAP_NMI,	xenpv_exc_nmi);
 #endif
 
@@ -563,7 +563,7 @@ DECLARE_IDTENTRY_DEBUG(X86_TRAP_DB,	exc_debug);
 #else
 DECLARE_IDTENTRY_RAW(X86_TRAP_DB,	exc_debug);
 #endif
-#ifdef CONFIG_XEN_PV
+#if defined(CONFIG_XEN_PV) && defined(CONFIG_X86_64)
 DECLARE_IDTENTRY_RAW(X86_TRAP_DB,	xenpv_exc_debug);
 #endif