drivers/rtc/rtc-lpc32xx.c: add device tree support

Adds device tree support for rtc-lpc32xx.c

Signed-off-by: Roland Stigge <stigge@antcom.de>
Acked-by: Rob Herring <rob.herring@calxeda.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>