x86: dt: Correct local apic documentation in device tree bindings

Until "x86: dt: Cleanup local apic setup" we read the local apic
address from the MSR and ignored the entry in DT. Reflect this change
in the documentation.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
LKML-Reference: <1298830419-22681-1-git-send-email-bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>