Add an RTC driver for the Dallas DS1742 RTC chip.

[akpm@osdl.org: cleanups, compile fix]
Signed-off-by: NAtsushi Nemoto <anemo@mba.ocn.ne.jp>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>