rtc: basic implementation of Epson RX-8581 I2C Real Time Clock

Provide the basic "get" and "set" functionality for the Epson RX-8581 I2C
RTC.  It currently does not support the RTC's Alarm or Fixed-cycle timer.

[akpm@linux-foundation.org: need log2.h for ilog2(), remove unneeded initialisation]
Signed-off-by: Martyn Welch <martyn.welch@gefanuc.com>
Signed-off-by: Alessandro Zummo <a.zummo@towertech.it>
Cc: David Brownell <david-b@pacbell.net>
Cc: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/drivers/rtc/Kconfig b/drivers/rtc/Kconfig
index 7951ad2..990020c 100644
--- a/drivers/rtc/Kconfig
+++ b/drivers/rtc/Kconfig
@@ -277,6 +277,14 @@
 	  This driver can also be built as a module. If so the module
 	  will be called rtc-fm3130.
 
+config RTC_DRV_RX8581
+	tristate "Epson RX-8581"
+	help
+	  If you say yes here you will get support for the Epson RX-8581.
+
+	  This driver can also be built as a module. If so the module
+	  will be called rtc-rx8581.
+
 endif # I2C
 
 comment "SPI RTC drivers"