rtc: add rtc-m41t80 driver

This is a new-style i2c driver for ST M41T80 series RTC chip, derived from
works by Alexander Bigga <ab@mycable.de> who wrote the original
rtc-m41txx.c based on drivers/i2c/chips/m41t00.c driver.

This driver supports M41T8[0-4] and M41ST8[457].  The old m41t00 driver
supports M41T00, M41T81 and M41T85(M41ST85).  While the M41T00 chip is now
supported by rtc-ds1307 driver, this driver does not include support for
the chip.

[akpm@linux-foundation.org: remove bogus `static']
Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Signed-off-by: Alexander Bigga <ab@mycable.de>
Acked-by: Mark A. Greer <mgreer@mvista.com>
Cc: David Brownell <david-b@pacbell.net>
Acked-by: Alessandro Zummo <a.zummo@towertech.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>