xen/acpi-processor: fix enabling interrupts on syscore_resume

syscore->resume() callback is expected to do not enable interrupts,
it generates warning like below otherwise:

[ 9386.365390] WARNING: CPU: 0 PID: 6733 at drivers/base/syscore.c:104 syscore_resume+0x9a/0xe0()
[ 9386.365403] Interrupts enabled after xen_acpi_processor_resume+0x0/0x34 [xen_acpi_processor]
...
[ 9386.365429] Call Trace:
[ 9386.365434]  [<ffffffff81667a8b>] dump_stack+0x45/0x56
[ 9386.365437]  [<ffffffff8106921d>] warn_slowpath_common+0x7d/0xa0
[ 9386.365439]  [<ffffffff8106928c>] warn_slowpath_fmt+0x4c/0x50
[ 9386.365442]  [<ffffffffa0261bb0>] ? xen_upload_processor_pm_data+0x300/0x300 [xen_acpi_processor]
[ 9386.365443]  [<ffffffff814055fa>] syscore_resume+0x9a/0xe0
[ 9386.365445]  [<ffffffff810aef42>] suspend_devices_and_enter+0x402/0x470
[ 9386.365447]  [<ffffffff810af128>] pm_suspend+0x178/0x260

On xen_acpi_processor_resume() we call various procedures, which are
non atomic and can enable interrupts. To prevent the issue introduce
separate resume notify called after we enable interrupts on resume
and before we call other drivers resume callbacks.

Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

drivers/xen/manage.c

@@ -46,6 +46,20 @@ struct suspend_info {
 	void (*post)(int cancelled);
 };
 
+static RAW_NOTIFIER_HEAD(xen_resume_notifier);
+
+void xen_resume_notifier_register(struct notifier_block *nb)
+{
+	raw_notifier_chain_register(&xen_resume_notifier, nb);
+}
+EXPORT_SYMBOL_GPL(xen_resume_notifier_register);
+
+void xen_resume_notifier_unregister(struct notifier_block *nb)
+{
+	raw_notifier_chain_unregister(&xen_resume_notifier, nb);
+}
+EXPORT_SYMBOL_GPL(xen_resume_notifier_unregister);
+
 #ifdef CONFIG_HIBERNATE_CALLBACKS
 static void xen_hvm_post_suspend(int cancelled)
 {
@@ -152,6 +166,8 @@ static void do_suspend(void)
 
 	err = stop_machine(xen_suspend, &si, cpumask_of(0));
 
+	raw_notifier_call_chain(&xen_resume_notifier, 0, NULL);
+
 	dpm_resume_start(si.cancelled ? PMSG_THAW : PMSG_RESTORE);
 
 	if (err) {