rtc: add support for the S-35390A RTC chip

This adds basic get/set time support for the Seiko Instruments S-35390A.
This chip communicates using I2C and is used on the QNAP TS-109/TS-209 NAS
devices.

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Byron Bradley <byron.bbradley@gmail.com>
Acked-by: Jean Delvare <khali@linux-fr.org>
Acked-by: David Brownell <david-b@pacbell.net>
Tested-by: Tim Ellis <tim@ngndg.com>
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>