rtc-ds1307: alarm support for ds1337/ds1339

Update the ds1307 driver with alarm support for ds1337/ds1339.  This uses
the first alarm (there are two), and matches on seconds, minutes, hours,
and day-of-month.  Tested on ds1339.

[dbrownell@users.sourceforge.net: add comments; fixup style, valid irq
checks, debug dumps; lock; more careful IRQ shutdown; switch BCD2BIN to
bcd2bin (and vice versa); ENOTTY not EINVAL.]
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Rodolfo Giometti <giometti@linux.it>
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>