x86/init: Add intr_mode_init to x86_init_ops

X86 and XEN initialize interrupt delivery mode in different way.

To avoid conditionals, add a new x86_init_ops function which defaults to
the standard function and can be overridden by the early XEN platform code.

[ tglx: Folded the XEN part which was a separate patch to preserve
  	bisectability ]

Signed-off-by: Dou Liyang <douly.fnst@cn.fujitsu.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: yinghai@kernel.org
Cc: bhe@redhat.com
Link: https://lkml.kernel.org/r/1505293975-26005-10-git-send-email-douly.fnst@cn.fujitsu.com

arch/x86/include/asm/x86_init.h

@@ -50,11 +50,13 @@ struct x86_init_resources {
  *				are set up.
  * @intr_init:			interrupt init code
  * @trap_init:			platform specific trap setup
+ * @intr_mode_init:		interrupt delivery mode setup
  */
 struct x86_init_irqs {
 	void (*pre_vector_init)(void);
 	void (*intr_init)(void);
 	void (*trap_init)(void);
+	void (*intr_mode_init)(void);
 };
 
 /**