x86: dtb: Add device tree support for HPET

Set hpet_address based on information provied form DTB

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Acked-by: Grant Likely <grant.likely@secretlab.ca>
Cc: sodaville@linutronix.de
Cc: devicetree-discuss@lists.ozlabs.org
Cc: Dirk Brandewie <dirk.brandewie@gmail.com>
LKML-Reference: <1298405266-1624-7-git-send-email-bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>