rtc: max8997: add driver for max8997 rtc

Add an rtc driver for Maxim 8997 multifunction chip.  Max8997 has rtc
module in it.  and it can be used for timekeeping clock and system alarm.
It provide various operational mode those are BCD/binary, 24/12hour,
am/pm.  Driver sets binary/24/ for default.  Maxim 8997 also supports
SMPL(Sudden Momentary Power Loss), WTSR (Watchdog Timeout and Software
Reset).

Signed-off-by: Jonghwa Lee <jonghwa3.lee@samsung.com>
Cc: Devendra Naga <devendra.aaru@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>