Add Dallas DS1390 RTC chip

v3 of this patch with some code tidying as per previous comments. Also only a single tx/rx buffer is used.

This patch adds support for the Dallas DS1390 SPI RTC chip.

---

drivers/rtc/Kconfig      |   14 +++
drivers/rtc/Makefile     |    1 +
drivers/rtc/rtc-ds1390.c |  256 ++++++++++++++++++++++++++++++++++++++++++++++
3 files changed, 271 insertions(+), 0 deletions(-)

index 9a9755c..7ec6abb 100644
@@ -292,6 +292,20 @@ config RTC_DRV_DS1305

This driver can also be built as a module. If so, the module will be called rtc-ds1305.

+config RTC_DRV_DS1390
+ tristate "Dallas/Maxim DS1390"
+ help
+ If you say yes here you get support for the DS1390 and probably
+ other chips connected with SPI.
+

+	  The first seven registers on these chips hold an RTC, and other
+	  registers may add features such as NVRAM, a trickle charger for
+	  the RTC/NVRAM backup power, and alarms.  This driver may not
+	  expose all those available chip features.

+
+ This driver can also be built as a module. If so, the module
+ will be called rtc-ds1390.
+
config RTC_DRV_MAX6902
tristate "Maxim MAX6902"
help

index 18622ef..6306900 100644
@@ -27,6 +27,7 @@ obj-$(CONFIG_RTC_DRV_DS1302)	+= rtc-ds1302.o

obj-$(CONFIG_RTC_DRV_DS1305) += rtc-ds1305.o
obj-$(CONFIG_RTC_DRV_DS1307) += rtc-ds1307.o
obj-$(CONFIG_RTC_DRV_DS1374) += rtc-ds1374.o
+obj-$(CONFIG_RTC_DRV_DS1390) += rtc-ds1390.o
obj-$(CONFIG_RTC_DRV_DS1511) += rtc-ds1511.o
obj-$(CONFIG_RTC_DRV_DS1553) += rtc-ds1553.o
obj-$(CONFIG_RTC_DRV_DS1672) += rtc-ds1672.o