rtc: add driver for DS1685 family of real time clocks

This adds a driver for the Dallas/Maxim DS1685-family of RTC chips.  It
supports the DS1685/DS1687, DS1688/DS1691, DS1689/DS1693, DS17285/DS17287,
DS17485/DS17487, and DS17885/DS17887 RTC chips.  These chips are commonly
found in SGI O2 and SGI Octane systems.  It was originally derived from a
driver patch submitted by Matthias Fuchs many years ago for use in
EPPC-405-UC modules, which also used these RTCs.  In addition to the
time-keeping functions, this RTC also handles the shutdown mechanism of
the O2 and Octane and acts as a partial NVRAM for the boot PROMS in these
systems.

Verified on both an SGI O2 and an SGI Octane.

Signed-off-by: Joshua Kinard <kumba@gentoo.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
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>
diff --git a/MAINTAINERS b/MAINTAINERS
index 6f2c849..d5ff4c3 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -2963,6 +2963,12 @@
 F:	drivers/input/touchscreen/cyttsp*
 F:	include/linux/input/cyttsp.h
 
+DALLAS/MAXIM DS1685-FAMILY REAL TIME CLOCK
+M:	Joshua Kinard <kumba@gentoo.org>
+S:	Maintained
+F:	drivers/rtc/rtc-ds1685.c
+F:	include/linux/rtc/ds1685.h
+
 DAMA SLAVE for AX.25
 M:	Joerg Reuter <jreuter@yaina.de>
 W:	http://yaina.de/jreuter/