x86/apic: Use lapic_is_integrated() consistently

lapic_is_integrated() is a wrapper around APIC_INTEGRATED(), but not used
consistently.

Replace the direct usage of APIC_INTEGRATED() and fixup a hard to read tail
comment. No functional change.

[ tglx: Made it compile and work .... ]

Signed-off-by: Dou Liyang <douly.fnst@cn.fujitsu.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: bhe@redhat.com
Link: https://lkml.kernel.org/r/1504774161-7137-2-git-send-email-douly.fnst@cn.fujitsu.com